Try the suggestions in this FAQ:
[Crash, exit or high CPU when viewing certain directories)
Turning off Shell Image Extraction is the first thing I'd try.
If none of that helps, you could turn off the option to generate thumbnails for all images (so only the images currently visible have thumbs generated), but from your description it doesn't sound like the problem is too many thumbnails in memory at once. It sounds like the problem is something causing a huge memory leak, and it's most likely a shell extension (in my experience) or possibly an Opus plugin issue.