Just recently, I run a Plex scan and my RAM usage on my ububtu box just keeps increasing until it falls over. On a 4GB RAM Ubuntu VM; I start a scan and it slowly creeps up and until its occupied all of my RAM and swap. rclone uses over 2GB and pledrive is using over 1.5GB.
I was having the same issue recently so I tried going back to Plexdrive 3.0. This seemed to be a little better, but still used a significant amount of RAM. I think root cause was me using --buffer-size=1G for my rclone mount. So for every file that Plexdrive was opening, rclone was trying to create a 1GB buffer in RAM . Removing this option significantly lowered my rclone RAM usage, and no longer crashed my server. Obviously, this is a temporary workaround. My thinking is that Plexdrive 4.0 is trying to open more files at a time than v3.0 was, leading to run away RAM usage. It looks like there is a new v5.0 beta out, but I haven’t tried it yet to see if it helps.
Not sure if this is the same issue that you’re seeing, but hope it helps.
Edit: Just tried out Plexdrive v5.0.0-beta.1498837265 with a 1GB rclone buffer and it didn’t run into any RAM issues. I would recommend trying it out to see if it solves your issue too.