Ah, your screenshow shows “Temporary filesystem already mounted”, so TMPFS is obviously configured.
You can try omd disable SITENAME; omd enable SITENAME; omd start SITENAME (instead of just stop/start). This should unmount and re-mount the tmpfs.
Or debug further with:
mount | grep /sites
df -h -t tmpfs | grep /sites
grep omd/sites /etc/fstab
ls -ld /opt/omd/*/tmp