This weeks 3.7.4 beta contains an automatic detection for the Fritz!Box 7590AX which turns on the fix that was already present in recent betas.
But yes, AVM did not fix the problem yet.
Because the problem is related to the power saving mechanisms the Smart Lock uses to run for months on 4xAA batteries. The fix we applied reduces the power saving and therefore works around the problem AVM introduced.
In general you can with 3.7.4 now reduce the power saving for all WiFis when setting the Smart Lock > Settings > Features & Configuration > Battery > Energy-saving mode to “Medium”. In the past this was restricted to the 7590AX (and alike) access points.