A lot of fixes were applied to the wlan.cgi code for what will be Core Update 190 to fix the sort of things that it sounds like you are experiencing.
Those fixes were also backported to Core Update 189 but it seems like for some reason they did not get properly implemented. I have looked at the backported changes and they seem to have been applied to Core Update 189 the same as they were to Core Update 190 but other users have had similar issues as you are describing.
I have a system running with Core Update 190 (Unstable) and that is running without any problems so the fixes in Core Update 190 seem to have fixed the issues but for some reason they have not worked properly with Core Update 189.
It might be worth reading through the following thread as some potential workarounds are described that might enable you to get a working system until Core Update 190 is released.
https://community.ipfire.org/t/core-189-update-hostapd-doesnt-start/13080