Can't proceed/find a door

If you start a BtSL game, is it limited by your progress in the main game? I got to a point where the wasn’t an obvious way forward and I hadn’t defeated any of the bosses.

EDIT: I should clarify that I’ve walked around the edges ot the current level several times and there doesn’t appear to be any secret doors (or at least ones that any of my party can detect)

No

The rogue-like version is independent of the main campaign. My guess, you have missed a door somewhere on the last floor.