Sure. 250 down/40 up.
Plex Server: 1.25.9.5721
Plex client on shield (same problem with Kodi add-on): 9.2.0.32520
rclone mount PD: /data/plex --allow-other --dir-cache-time 1000h --syslog --syslog-facility LOCAL5 --log-level INFO --poll-interval 15s --umask 002 --user-agent="GMount" --rc --cache-dir=/data/vfscache --vfs-cache-mode full --vfs-cache-max-size 820G --vfs-cache-max-age 9999h --vfs-read-ahead 1G --buffer-size 80M --disable-http2 --tpslimit 10 --tpslimit-burst 10 --bind 172.16.20.50
Yesterday I noticed stuttering with another client as well on the test file in question. It is considerably less than on the shield however. So it might be rclone "related" after all. As you noticed correctly: No problems whatsoever when the file is locally available on the plex server. I can only suspect that as a result the server itself and the connectivity between Plex/Shield is not the problem.
When I look at bandwith consumption on the router while playing I can see bursts between 60-150 Mbit/s in download which would be consistent with the MBit of the testfile. I assume that there are bursts but that is what the read-ahead should be for should it not? When I do not watch the testfile but copy it from the rclone I get a consistent 240-250Mbit bandwidth consumption. So rclone COULD get the file with 250Mbit/s. It (Plex + Rclone) just chooses not to. Which again as long as the read-ahead is filled should not be a problem. But it is in real life...
Maybe it is related to this:
Vfs-read-ahead not working? - Help and Support - rclone forum
I believe that was my first attempt to fix things last year. If it is the same thing: Why is the client (direct play) or the server jumping around instead of reading a consistent stream?