I am having a weir issues when trying to export an object to a game, causing the UVs to be partially inverted. In blender the normals look fine, however in game only part of the normals appear properly (see attached images, top shows expected from blender, bottom shows actual result from game).
I have made sure all transforms are applied, tried Apply Transform and multiple combinations of export settings, however I can not figure out which setting to change to fix this. I know it is possible to fix this in the export settings, because I have got it working multiple times in the past. Unfortunately, those times appear to be flukes because I can't get it working again.
Could anyone tell me which transform/setting in the obj/fbx exporter this issue is related to? I'd really like to understand why this is happening.
Edit: I've added a picture showing the normal direction. I was also planning on adding the .blend file via blend-exchange, however I cannot actually post it because I do not have the rights necessary to distribute it as required by blend-exchange. This makes the problem even weirder because this model was ported directly from the game, had its UV-layout slightly modified (1 island with flat normal map moved a tiny bit), and then had this issue when exporting.
I've also added a drawing to clarify how the bevels appears to look vs how they should look from a sliced perspective (bottom picture, left how it appears, right how it should appear).
Edit: I've now included the model without shading (top) and my normal map (repeated) with UV-islands overlaid (bottom). The normal map has a size of 512x512 and is the same as used in the game. Note that the square on the top left of the UVs is separated onto a different texture and is irrelevant to this question (because I don't see any wrong normals on it in game).
I also wanted to clarify that this model has been imported from the game's data, has been modified (the island in the top left was shrunk to accommodate for more icons), and was then exported successfully on one occasion, which I can not reproduce.