I had something similar today.

The quest where the Captain has you go into the hold, to recover blasting powder.
To then use the cannon and kill the giant, who is along the shoreline.

IWT didn't want to work, in the hold.
Basically used follow to get them kind of close.
Then hit my up-arrow key, which is independent slave forward.
Which moved them into range.

Without any changes, as soon as I was on the shore/island, IWT worked exactly as expected.