If the communication is not working properly a restart of the integration might work, but not in this case.
Bur you are right trying to restart the MQTT feature on the lock side does not work.
Anyway - I have played around with the battery power mode, but both locks have the same setting (automatic) and the same FW (4.2.8).
I will monitor this on my two locks and will report back.
I guess I will need another 1-2 weeks to get reliable results though.
In the past one of the locks went to unavailable and it took sometimes several hours (I suspect the Wifi repeater re-initializing to trigger a re-connect).
For now I can say, that the recent disconnects (3 since the update) have been resolved within 10 seconds - so I am positive that the MQTT connection has improved.
By the way, the NUKI App in these cases still showed the Wifi connection to be ok (so did the router).
So, it was obviously just the MQTT communication.