We have no route filters.
I fear that if we disable friendly URLs, not only would things be less friendly, but current links might break.
I just went on my test board and added /forums to the end of the board URL & Home page URL, it's installed on the root. It does in fact work clicking around the board and it shows as /forums/ now, perhaps that's the issue? Check those inputs and see if you can remove /forums/ from it, if it exists there.