SLZB-06 / z2m broken after SLZB06-Firmware update 3.2.7

Updated firmware of the SLZ-06 today to 3.2.7. At first everything seemed to be fine, but after a maybe 2 hours the zigbee network became unreliable and is full of "MAC_CHANNEL_ACCESS_FAILURE" warnings.

Downgrading to the previous firmware 3.2.0 did not help. Reboot of z2m oder SLZB06 did not help.

Some advice?