In the livery manager, I can see the images for all the A318  CFM liveries. However, The A319 CFM & IAE images for all the aircraft's minus the ones I have installed don't show up. Upon further investigation, I found the thumbnails missing for all those aircraft in the simobjects folder for each livery (even after a clean reinstall). What could be the reason for this and how to fix it?

I think the main reason is that P3d V4.3 does not use thumbnail files any more. 

The a318 has thumbnails and I still see those in the livery manager, also if I add a livery I see those too. I have an Air Canada Rouge A319 CFM and I can see it, but not the other CFM liveries that came with the base package.

As Mathijs said, P3D doesnt use thumbnails anymore and therefore new repaints do not contain them and and thats the reason why you don not see them.

Ah ok, didn't know that. My misunderstanding.

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