I was having an awful time with the new network manager and kept having hotspot problems. Messed with it for a few days and in the end installed a fresh version of OP4 and then first thing set up all of the localization /wifi country stuff and then created the hotspot first thing before any modifications/updates to OP4.
Not sure if that is what did it but it has been bulletproof since. Also not sure if you know this and I had a hard time finding any instructions but you need to go to the network manager and check connect automatically in the general tab.
Left Click Network Manager>Edit Connections>Select Hotspot and then settings button (gear)>General
On a side note, OP4 doesn't seem to be so particular about it on a Pi4.
Not sure if that is what did it but it has been bulletproof since. Also not sure if you know this and I had a hard time finding any instructions but you need to go to the network manager and check connect automatically in the general tab.
Left Click Network Manager>Edit Connections>Select Hotspot and then settings button (gear)>General
On a side note, OP4 doesn't seem to be so particular about it on a Pi4.