Most mods are not compatible with one another, so that is almost certainly the reason. More likely the gallery unlock mod than the walkthrough mod as it probably changes the heart menu.
Yes the mod doesn't know what actions you have already taken in the game. So you need to do the actions that unlock achievements on a modded save (but once you do them it will remember them across saves!)
been replaying the game, really love the mod! add a whole more gaming vibe to the game. Btw, the first achievement wont be unlock in the gallery, even though I get it, I even try a few time.
