This same thing happened to me on our last trip. I was so thankful that the cast member thoroughly explained the issue to me! I had nearly 20 active bands on my account and he told me I could keep amassing them if I’d like, but to have
no more than 9 active bands at one time if I wanted to have all of my magicbands working properly. Basically, every time you tap, the system only recognizes “the top” 9 active bands and the one you’re using must be one of those 9. But! The next time you tap, the system has shuffled your active bands and a new 9 are on top. This is why re-tapping generally solves the problem with a glitchy band.... it’s just got to be shuffled into the top 9 and then it works!
You can, of course, deactivate and reactivate your magicbands easily through
MDE... you never have to kill one off permanently.
So, although there is no limit on how many you can own, you should keep an eye on how many you have active.