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To clarify, a “crack” sound could originate from many parts of the drive train (pedals, BB, etc). The sound I am attempting to describe only occurs once after shifting to any of the 8 to 14 gears and applying significant force to the pedals. After the crack sounds, continued pedaling or coasting and then putting much force into the pedals never causes the sound to occur again…..until shifting to a new 8-14 gear.
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I have run out of ideas that would be unique to a Rohloff.

A strange thunking or clicking noise in a drive train can be hard to find.  Noises I have had that I was sure was in a bottom bracket or pedal area, or that I have heard others describe include:

• A clicking noise in a pedal, this was unusual because it was where I thought the noise was from. Sometimes, once per revolution.  Added grease to the pedal.   Fixed.
• Clicking noise in a bottom bracket.  Once per revolution.  I finally bought a new bottom bracket.  When I pulled my crank arms off the old one and then started to unthread the non-driveside bushing, it felt much looser than it should have been.  Instead of swapping bottom brackets, I tightened it.  That fixed it.
• Clicking noise when pedaling hard, twice per revolution.  A rear rack bolt that was tight, but not tight enough.  When I pedaled hard, there was enough frame flex that the stiff rack moved a bit under the bolt.  I diagnosed this by standing next to the bike, one hand on bike saddle, other hand on the rear brake lever holding brake hard, and one foot pressing on a pedal, then I could hear exactly where the click was.
• I have heard of others that solved a clicking noise by greasing a seatpost, the seatpost as they pedaled moved enough inside the seat tube to click.
• Loose square taper crank arm.
• Loose headset, but that noise should be from a location that you can't confuse with a rear hub noise.

I am sure that I could think of other issues, but none come to mind right now.

I assume this is chain drive, not on a frame capable of belt drive.  But if it is on a frame capable of belt drive, I would make sure the frame fittings for changing a belt are tight.

Being on a tandem, you have two bottom brackets, two cranks, that is more opportunity for places to make strange noises.

I know my list above is not specific to shifting, but it is all I could think of.

After posting this, came up with one more idea:  Loosen your shift cables slightly, maybe two or three turns on the cable adjusters.  Point being that if your cables are too tight, when you shift, the shift mechanism might not fully seat in the correct place inside the hub.

There is the Sunshine coast trail that you could start in Vancouver and it returns back to Vancouver and you can go via Victoria also take a look at the Kettle Valley trail in British Columbia as well. Without a vehicle at either end of trips here in Canada is a pain as we don't not have a decent public transport system like Europe.
I am from Yorkshire but have lived in BC for 47 years and come back to the UK for bike touring and have rail pass to duck out on the hard or wet day. I am off back to Scotland again this summer via visiting family in Yorkshire with a month long rail pass.

This is an immaculate model I purchased back in 2019 with the intention of cycling to Australia. Sadly, it managed only Lands End and Edgbaston for the cricket! It's been in dry storage ever since. The frame Geometry apparently suits someone in the 5'10'' to 6'5'' range.
It has very smooth 14 Speed Rohloff Hub gears, dynamo lights & a Brooks leather saddle. The front and back racks allow an ample load & there are lots of extras like crucial spare parts and front suspension forks if you wanted more 'off road'. SPD shoes thrown in if you're size 45. I'll possibly sell the Ortlieb panniers too. Photos should be attached hopefully.
I'm located just north of Bath in Malmesbury ( SN16 postcode ). 07500 657918. Offers close to £2000 considered.

People stop me to talk about my electric bike. The most dire problems I come across can all be traced to a misconception, an attitude. Because I don't suffer from the same deluded expectation, I still have the battery from my first electric bike, in perfect working order after near enough two decades, because I take care never to discharge it fully, and to charge it after every trip no matter how short.

They didn't get the memo that what they intend buying, or have bought and killed by ignorance and careless neglect, is not an electric motor-bike but an electrically assisted pedal bike. Consequently they repeatedly run the battery flat without pedalling and then wonder why it dies in short order and won't hold a charge any more.

Because they aren't normal cyclists, because the electric bike is their first bike, they don't have the normal cyclist's acceptance of the necessity of bicycle maintenance. They don't understand that the only way to avoid expensive wear and tear is routine maintenance.

Then there was the outraged lady who complained, 'I've recharged the battery as religiously as you advise, but I haven't lost an ounce since I started cycling. Instead I've put on eighteen pounds, more than a stone.' Yup--and nobody ever saw her turn the pedals even once, though she's probably got muscles in the thumb used to squash the thumb throttle down flat.

Some form of Maoist re-education would perhaps answer to what's in fact all the same root-problem. If people were not allowed to have electric bikes until they've ridden a year on a derailleur bike and another year on a hub gear bike, something like the pyramid of motorbike engine size licences one has to go through to be permitted to take a Hayabusa on the public roads, they would perforce learn about simple maintenance, and the correct habit of charging the battery when it is best for the battery and not most convenient for the cyclist will, we hope, become ingrained.

Quick tip: the fastest, cheapest way to bulletproof your bike electric motor is simply to replace the plastic gears inside with steel gears, which are cheap enough to install as an experiment to discover whether you can live with their additional noise. Or you can pretend you're a master artisan, a fitter and turner with an emery cloth sticking out of your rear pocket, and stone and fit the gears until they're quiet.

You can fireproof the controller against the same problem of excess heat (higher currents melting inadequate plastic sheathing) by making up a wiring harness of higher quality wires (the insulation has a heat rating, the higher the better) and fitting it.

I also am inclined to leave bad reviews for failures, but don't take the time to write a review if it is as described.

On that youtube video, some of the polls were how many motors were replaced under warranty, or were otherwise replaced.  That is a much more accurate way to do an analysis.  I can imagine a lot of people write reviews on e-bikes complaining they wanted more speed and more acceleration and more range, such reviews mean little.  But a motor replacement is only done when needed.

I usually look at the 1 or 2 star reviews first, and I take into account how prevalent those poor reviews were, e.g., were the ones and twos 5 percent of the total or 45 percent of the total.  Sometimes I was inclined to order something on line, but after reading some of the poor reviews if there were a lot of them, and if they were for the same manufacturing defect, I suddenly decide that I really don't need that item after all.

One of my neighbors is a bike mechanic at a bike shop on a large university campus.  He said most people on campus that bring in an e-bike for some reason or other has clearly just left it in the highest gear on derailleur bikes.  They get on the bike and aim for maximum motor assist with the least amount of pedaling effort.