I'm affected by this bug as well.
I didn't track exactly which plugins lost their thumbnails, but I can say for sure that a few of my iZotope & UAD plugins did. I didn't notice it for plugins from other companies. Interestingly, not all plugins from these 2 manufacturers seem to be affected, either (well, on my machine, that is). Here are some examples I'm confident about:
NOT affected (did not lose their thumbnails)
- iZo Ozone 8 EQ (and, I believe, the Dynamics module is persistent as well)
- UAD Lexicon 224
Affected (did lose their thumbnails):
- iZo Neutron 2
- iZo Neutron 2 Mix Tap
- UAD Eden WT800
- UAD Fairchild 670
- UAD Tube-tech CL1B
- UAD Shadow Hills Mastering Compressor
- UAD Oxford Dynamic EQ
I'm on Win7, using Studio One 220.127.116.11910 Win x64 (Built on Mar 20 2018)
Please fix this bug - it's really annoying! With large plugins collections, I find that even the folder view gets crowded, and as such thumbnails are a crucial tool to still find plugins reasonably quickly.