CacheManager... I run it and it after a few minutes say it is done. However, spinner in browser tab is still spinning, and
if you look at the cache folder it is still processing.
Should this be saying it is done? I think if I move from that page, then remaining caching stops.
It depends which mode you selected. One is printing the images diirectly on the page (legacy) and the other one (cURL) sends requests to do this basically in the background. The first is not always reliable but works better on some servers.
This is a very heavy task that is started in - simplify - chunks in the background and depending on the number and size of your albums and images and the number of sizes to generate. The more the more it might take a while more. On large sites this can take a few hours.