ZigBee bulb cycles between unavailable and On when powered off

I have noticed that a seldom used ZigBee bulb connected using ZHA shows up as On every two hours (actually 118 minutes), then unavailable for another two hours and repeats this cycle. The bulb is powered off at the wall switch.

Is this expected behaviour with ZHA?

It’s an IKEA Bulb ( TRADFRI bulb E27 CWS opal 600lm) and the coordinator is a Texas Instruments CC2531 dongle. However, given the bulb is off the entire time it seems more likely to be related to software.