After updating from 1.1.6 to 1.2.1 my old Tiled maps seemed corrupted in a very strange way. Object layers containing text displayed numbers all wrong, replacing unique numbers with some generic ones. Object layers that contain only text (not numbers), showed just fine. I uninstalled 1.2.1 and reinstalled 1.1.6, and the numbers are fine. So the problem appears to be with the new version of the Tiled app and not with the map files themselves.
I’m using Tiled on macOS 10.13.6.