What about making 3 configs: 1) "Glued" - basically leave everything as it is now 2) Medium - make straps weaker so you can detach excavators using some force 3) Light - if its even possible make excavators fully detached immediately after spawning so they can easily fall off the flatbed (after sharp turn on relatively high speed, after side impact, etc.)
Because your game is outdated. https://wiki.beamng.com/Updating_the_game From wherever you bought it.
He could have been updating and hit the pause button by accident. I had me game stuck at 12.0.1 and then I updated yesterday.