This console error happens every time someone joins the server.
This is my default-assitgnment in the conf file.

The guest group has only five nodes. Is there a way I can instead put those nodes directly on the default group on the database (then I can just get rid of guest) or is the way I'm doing it better?

LP 3.1.51 (You're probably going to suggest updating to 3.2.7)
Spongeforge 5.2.0 Build 2344

Update
I got this error when checking an offline player

You need to wrap 'group.default' in angle brackets, like: '<group.default>'

And yeah, you can just set those permissions directly onto the default group.