I built up on the log near the stump. I'm now being raided there for the 1st time - but weavers. They can't  get up  to  the base, & I  can't find any of them down  below. The raid won't end, & I can't camp out & save progress.

Is there seriously no way to resolve a raid that gets messed up like this? o_0

I had a similar problem with:
1) A base A up the slopes of the woodblocks near the Axe/Survey Station in the Logpile area
2) A base B under the book on top of the Picnic Table

NOTES:
Base A: Larva cannot reach this base. Ants can. Larva raids eventually complete after 10 minutes with the message "payback delivered" or "base defended"

Base B: Had a Larva raid last night. Music played for what seemed 15+ minutes, thinking it was a glitch. Eventually I had a message, "remaining payback lost interest" - bloody brilliant Obsidian!!! Love it!!

With Base B it would seem that there is error code to prevent raids from going on indefinitely

What happens when you exit and reload the game? Have you resolved your issue?
 

 

I had a similar problem just now with a larva raid, I didn't see any and my main base was the target. The game then proceeded to tell me payback delivered when there was no damage caused. When a raid can't reach you does the game just RNG the message?