Not sure if this is intended or not, but I just had some green spitters (bobs, rampant or NE, not sure which) spawn way back at the mangroves when I was killing stuff on the front line.

Is this something intended, where I have to defend the mango waters?

It's not intended, but Ribbon Maze doesn't touch biter/spitter spawning. So this will be a bug in one of those other mods. Do you have a copy of the save before it happened that you could share?

Unfortunately, no.

I'll try to grab an autosave if it happens again.