Hello Luke Dave, welcome to Microsoft Q&A forum.
CurseForge and modded Minecraft troubleshooting falls outside the scope here (the Microsoft Q&A forum covers Windows and general Microsoft products). For issues like this, the best place for support is r/CurseForge or CurseForge's official support—they'll know the mod-specific issues better.
If you want to rule out account-level restrictions first, check your Xbox Privacy Settings at https://account.microsoft.com and make sure "You can join multiplayer games" is enabled—sometimes that causes similar restart prompts. I hope this helps point you to the right direction.