Just recording this in case it’s useful to somebody in the future (probably me).
I have 6 v1 Hue Dimmers and the one in the bathroom stopped working because the battery went from 100% to zero. I suspect with network issues these devices chew through battery trying to find it, as it’s happened to me before. It didn’t come back automatically after replacing the battery so I paired it to ZHA again. This is when the trouble started.
Once it was paired, buttons 1 and 4 (top and bottom) were doing nothing, and buttons 2 and 3 were only sending “step” events. On my other dimmers this was normally followed by “short press” and “short release” events. Trying to pair again resulted in ZHA showing “Configuring” and not moving onto the next step.
I got it working again by removing the device from ZHA, restarting HA for good measure, and pairing it again from scratch. Of course it took much longer than that because of trying it right beside the Zigbee dongle a few times before doing it again in the bathroom where it belongs.
This is not the first time I’ve had problems with these. But that could be extended to a lot of v1 hardware and Zigbee in general.