Plex keeps grouping two different movies as one, even when using {tmdb-id} in directory name

Have you tried adding the source id to the filename rather than just the enclosing directory/folder? Like this:

Be My Master (2018) {tmdb-592742}\Be My Master (2018) {tmdb-592742} [1080p x265 AAC].mkv

I’m not sure but I think I remember during the development of the new movie scanner that it pays heavy attention to the actual filename rather than the enclosing directory.

You might want to move the directories/files out of directories that Plex is monitoring, do the Plex Dance and then try adding them back one by one.

Good Luck,

Chris