One thing obviously different when you were on vacation is that you didn’t use the wifi router at home. I think you said you switched to 5 GHz and it seems to have helped. But it didn’t solve the random reboot issue altogether? If not, there’s a possibility that your router is generating some kind of interference (maybe with or without the TV Adapter) that causes the OPN S1 to reboot.
The issue you have with connecting to the ON app on your new iPhone is a different issue (connection issue) so if you had the new iPhone with you on vacation and it didn’t reboot then it just established that it’s a different issue and not inter-related.
The other factor is the TV Adapter 3.0 which you didn’t have with you on vacation. You did say that you had experienced reboot when or when not using the TV Adapter before. But one difference is that when you’re at home at didn’t use the TV Adapter and still had reboots, maybe the TV Adapter was connected to power and maybe even turned on, even if you didn’t put your OPN S1 in the TV Program mode. So one thing to try is to make sure the TV Adapter is removed from power when you’re not using it.