GL-MT1300 firmware 4.3.7 r4 not working in repeater mode

yesterday I installed firmware 4.3.7 on my Beryl, chose not to keep the settings and even did a factory reset afterwards.
Since then, it is very unstable when configured in repeater mode, especially when 5GHz ist turned off.
Most often I can see the WLan, can connect to it and my laptop even gets an IP address, but the connection is practically dead, I cannot even ping the router itself.
This practically renders it useless because I heavily rely on the repeater functionality.
Steps to reproduce:
Configure a 2.4 GHz WLan, connect to this WLan, enable repeater mode and join the to-be-repeated Wifi, do a power cycle of the router.