There seem to be a problem with onCollision and new custom objects
When a custom object that does not already exist in the play-area is loaded (taken out of a container/state changes/ and when spawned probably too), a onCollisionEnter/Exit check is triggered for every other object in the playing area.
It does not matter if those objects are colliding with the new object or not.
Totally unrelated objects get triggered.
Not randomly, I'm talking all other objects.

I managed to isolate the problem and do an example save game:

In the save file there are containers and other objects ("boards and notecards and a tile"). The "other" objects all have a onCollisionEnter/Exit scripted to them.
The script just logs the name of the object and and event.

When the game is loaded all of those trigger,so log gets a log entry for each object and each event once.
This is expected and ok.

But try to take out the "uboat"-chit (custom object) from the containers.
Check the log after that => all objects have reported a collision Enter/Exit even if there was no collision.

This does only happen if the object does not already exist in the play-area.
So if you leave the object on the table and take another "uboat"-chit out, no onCollisions events are triggered.
But once you clear the table of chits, retaking one from the containers trigger all onCollisions events again.