7.4rc2 Wifiwave2 "group key time out"

I know Mikrotik’s “Group Key Timeout” has been discussed in all aspects in various posts for NON-wifiwave2 SW.

But in 7.4.rc2 and wifiwave2 it is supposed to work as it is using standard chipset wifi drivers.
But still I see on Audience log massive amount of these ones at all kind of signal levels (good and bad) from many clients:

XX:XX...@wifi3 disconnected, group key timeout, signal strength -69

Sometimes every 10 seconds sometimes every minute.
The group key timeout is default, according to wiki it is 5 minutes.

I could imagine, that its not key time out, but rather “loost connection” and the log message is always the same.
But at signal strength -69 there should be no disconnect!

What is the advice from the experts here?
(PS: I do use 802.11r aka “FT” mode enabled on my interfaces)