deCONZ and Symfonisk is unstable

I’m using deCONZ / Conbee II for Zigbee, and Node Red for automation.
I have 3 IKEA Symfonisk controllers. One works very well, and has been working for a long time.
But the other 2 only work for a limited time after they’re added.
They stop working after a few minutes or after two days.
Sometimes they work for a little while if I remove and insert the battery, but not every time.
There’s no deConz message in NR. I’ve tried listening to the deconz_event in dev.tools as well with no luck. The working one sends events, but then others don’t.
Only one of the two show up as available in the deCONZ UI, but neither of them work.
All my other Zigbee devices (92) work fine.
What can I do or try to make them work?