if you are try deleting your cache in the preferences folder : media & disk cache - both options. this is more than purging disk cache. see it that works.
You mean doing the Preferences>Media & Disk Cache > Conformed Media Cache > Clean Database and Cache and Empty disk Cache on the same page? That didn't fix it, it seems like.
yes. clear both of them and restart your application
if that does not work, Manually delete the files in both the Media Cache and Media Cache File folders:
macOS: /Users/user name/Application Support/Adobe/Common/Media Cache and /Media Cache Files
if that does not work -> reset your preferences Cmd+Alt+Shift and click twice when you launch the app. there will be a dialog box - click o.k to reset preferences. clear the cache again in the same method afterwards.
I was out for a while so didnt have a chance to test it. I did all of the above, but it is still happening. In fact, it is even rendering the strange frames into the final .mov files...
cache has got a hold on you. see this thread: "Stuck" Image in Transparent Background maybe you could find some useful advice there. some suggest it has to do with GPU. I would try install the latest driver or uninstall it if it's the latest. have you tried resetting you preferences? Reset After Effects Preferences