Black metals only with packed maps - sRGB Issue

Hi there.

I’m using a decal oriented workflow and I’m having peculiar issues related to toggling the packed (ao/rough/metalness) maps from Painter to UE4.

Generally I find I understand the issue and simply disable sRGB on the texture once imported to UE4 with great results.

However the image below shows the exact same packed texture only the one on the left is packed on to a large 2k atlas and the other (right) is a stand alone 512k texture. The one on the right is correct and was wondering how I would go about resolving this issue with the decal on the left? I have also shown the atlas packed texture sheet and standalone as they are in engine. I have confirmed the wrong texture hasn’t been used by copying over the atlas (problematic one) and replacing the larger packed with this scaled up (poorly but hey just testing!).

I assume because I am merging these onto an atlas in Photoshop UE4 tries to almost average the values and disable sRGB accordingly? I’m really not sure at this point but I have tested toggling sRGB on for the decal showing the correct results and it shows an almost identical black shaded problem thus confirming it’s something to do with the sRGB being merged when disabled across the atlas?

Thanks for any help this is infuriating and really affecting our workflow.