I was making a post about encountering the same issue, so I'll add it here.
I played Forgotten Sanctum earlier today and when I came back for more, Steam updated the game. Now my saves from today aren't working anymore. The loading button has the text "Missing DLC" and identifies the supposedly missing DLCs as LAXH and LAXI. The saves from yesterday, also made while playing Forgotten Sanctum content but a lot earlier, are still available.
I saw an earlier similar thread where the recommended solution was to create a folder named "LAX[number]_exported", so I tried that with folders called laxh_exported and laxi_exported, but it didn't help.
I own all the DLCs and have everything installed except the Critical Role pack. The game's version is v4.0.1.0041 LAX123ABCDFG -steam.
I'm playing on Windows Professional 7 64-bit, if that matters.