A couple weeks ago my speedometer stopped working. The display was working fine and no indication of a low battery. A month before I had a similar symptom and replaced the battery in the sender which fixed it. So very unlikely that it was a low battery again. I pretty much gave up and decided the universe was telling me that less electronics is the way to go.
While I was out for a short spin today, I thought, hmmm, did I really check that magnet carefully? So I stopped the bike and took a careful look. Aha! The magnet was aligned to reach inward from the spoke, away from the sender. So I just reached down and twisted it 180 around the spoke, so it would pass close by the sender. Voila! Now it works again.
Simple is good!