It’s because you’re disconnecting from your session most likely.
Do not run a script or the rclone command using the & to send it to the background. This is the unstable way of doing it.
There’s an easy way to test this, try this:
screen -dmS rclone rclone mount …
Put your options after mount and execute. It should stay running indefinitely.
I believe @Ajki has a script he posted to also run a cron job script every minute to check if it’s still
Mounted and if not, remount. I use one too but not at home at the moment to be able to pull it out.