I've noticed that since the new update backup you call is now actually basically glued to the ground and cannot move. They are attempting to drive forwards but jolt very slightly then let off the accelerator. They repeat this in a cycle until they either automatically give up or because I have Ultimate Backup installed, they'll turn into a buddy I can manually dismiss. On rare occasion they will free themselves and move but I've only had 3 units out of around 100+ backup units I've tried calling do it.
For additional information, I have tested it with both the built-in LSPDFR backup menu and the backup menu that Ultimate Backup has and the issue is present using both menus. I also cannot actually ram them either, as I said, they're basically glued to the floor and are immovable.