None of the cache mode cache to RAM as that's not a thing.
I'm not seeing anything wrong in the logs as that's what I would expect to happen.
The only thing that uses memory is buffer-size as that is how much of the file is kept in memory. Buffer is dumped if the file is closed.
That's not how the cache mode works. This only writes files locally to disk and uploads them. This is used for certain applications/programs that need a more compatible file system to write to. You'll see an error in the log saying you need this if the program is asking to write in a mode that isn't compatible with off.
Both OS'es do the same thing here. It's more dependent on how the file is being accessed. If the file is accessed sequentially, it continues to read ahead based on the buffer size until it's closed out. If you are using full, vfs-read-ahead comes into play as well.
I'm not sure if minimal uses sparse files as it's not called out as I've never used it or found a need for minimal.
Full cache mode definitely uses sparse files so you'll see a difference in what is being reported and what is actually used:
felix@gemini:/cache/TV$ du -sh *
499G vfs
3.5M vfsMeta
felix@gemini:/cache/TV$ du -sh * --apparent-size
2.4T vfs
376K vfsMeta
as an example as I'm using full so files are sparse which means only parts I've read are 'filled'. No idea how Windows shows that offhand as I'm primarily a Linux user.