What rclone settings are you using? What does your local system resources look like when it is running? (Particularly CPU & RAM.)
I'm using the web-based beta CLI because I have too much trepidation to use it in Terminal. I had tried it in its default settings with only my app keys/paths assigned, and it actually caused a huge screw up: for whatever reason, it wound up renaming hundreds of files on the B2 bucket with garbage characters, meaning that those files' internal paths are ruined, so I had to wipe all the affected ones and re-upload with a different client (Syncovery, the only one which is stable). I don't think I want to muck with it again.