The way paths are stored have changed. Re-assigning the asset to the advert will solve the issue. For some users the migration script doesn’t work. But for the majority of people it worked fine. I don’t know why it didn’t for you…
And yes, pathing was fine already, but some people with non-standard setups had issues because AdRotate didn’t follow the standard method in WordPress. Which in itself was fine also, unless you required stuff to be in certain locations.
There are a bunch of topics elsewhere on this forum about that.
At any rate, it’s not a bug, just a unfortunate sideeffect of a fixed “problem”.