I did it like this:
Select a group of objects -> move the group of objects to an intermediate point -> mirror the group of objects -> move the mirrored group from the intermediate point to the primary one -> deselect. Result: they fly to the intermediate point and the mirroring is reset.
I am attaching a screenshot of the initial base and the final stage; as you can see, everything is fine with the tiles. Maybe the number of objects is too high?