I rechecked: the problem does not depend on the availability of national symbols.
So, any ideas?
Jooster, sorry, I don't understant your solution.
I'm also having this problem in a gallery. The label fields are not displaying any text in Play mode. Interestingly, I have a checkbox control in the gallery and that is displaying the correct value/check. The correct number of records is also being output to the screen. Same on iPad, Windows desktop.
In Edit mode everything works ok.
Sounds similar. Only noticed it today (2019-01-20).