I can confirm that the reconnect problem still exist with firmware 7.57 for the FritzBox 7590AX.
Firmware 3.7.7 for the Smart Lock 3.0 has just been released. It contains the fix that has already been in beta and solves the problem temporarily. There is no need do change any settings on the Smart Lock. Just update the firmware.
We continue to work with AVM on eliminating the root cause of the problem at their end.