Hlorandus' sewer exit should probably be updated to use T_De_DngStrongh_X_Sewer_01 with ex_vivec_grate_01 now that we actually have a dedicated sewer exit for the set
There's two sewer entrances in Firewatch exterior that are just using the interior trap door as the door. It looks jarring and wasn't intended like this during the int development. Instead, a more fitting asset, e.g. T_Imp_DngSewersMw_X_Grate_03, should be used, but it was also discussed that there possibly should be a dedicated grateless sewer hatch asset so that the grate can be added separately as the door.
This is a vanilla mesh, but it is not used in the original game, so I don't know if this is something that should be fixed by the Patch for Purists or not. Morrowind Optimization Patch also covers some unused meshes, but that hasn't been updated in a long time. Anyway, this mesh is used in a couple of places in TR, so the issue mainly exists there (and in other mods that use this mesh).
Many treasure chests used by int devs have static loot, or have pretty boring loot overall. There should be a few chests with randomized item types and value levels that can be placed.
This is a good opportunity to add in more TR-specific items without needing to be hand-placed.
Grimdil (TR_m1_Grimdil) in Bal Gernak's Manor in Llothanis is missing some wares that he's meant to sell, as Yimanalor (TR_m1_Yimanalor) in the neighboring room owns most of the items on Grimdil's bookshelf and table. These include soul gems and enchanted items that Yimanalor can't sell, being an alchemist.
Also, there's also an egregious floating lantern on top of Grimdil's wardrobe.
I've come across a bunch of NPCs who have the useless Weakness to Corprus Disease spell, including the misnamed 'Corpus' one too. They could probably be deleted or swapped with more appropriate Destruction spells.
If you acquire the thief's journal before starting the quest, the quest is added and advanced to stage 85: "I found the thief's journal. It might be enough to prove Marlene's story."
This journal entry does not make sense because you have not met Marlene, nor do you know what her story is, nor why you should want to prove it.