I don't see any obvious mistake here, but...
I have always been a little unsure about which of the two remotes the --drive-server-side-across-configs the flag will apply to in this syntax (or possibly both?)
Open your rclone.conf and insert this at the bottom of both your Gdrive remotes:
server_side_across_configs = true
Then save the config and try the command again (you will not need the --drive-server-side-across-configs flag then, but it won't hurt either - just redundant).
Does that work better?
Note that the easiest way to check is probably to enable verbose output with the flag:
and then each copied file should have (copied server-side) at the end of the line if it is working correctly.
Also check if there are any ERROR lines.
I also highly recommend you use the latest rclone version (currently 1.50)
Many users use old versions from repositories on Linux especially, and there have been a LOT of improvements to this in the last handful of versions. Easiest way to check your version is to run:
Easiest way to get the latest version straight from rclone is
curl https://rclone.org/install.sh | sudo bash
Test and report back