You are in the Label text edit mode.
Just press enter to leave it. Space bar or play in general will now work.
You can also assign an alternative key combination to play (in preferences).
It must be a combination that does not represent a character or number. My assignement is for example Ctrl-Space. This will not alter the behaviour of the space key - it will still work to play and stop tracks.
Additionally, you can navigate between the labels by pressing Tab and Shift-Tab and play them with the new key assignement.
You are welcome.
I guess that you now press enter before playing. Or have you tried the additional key combination too?
You can of course also click on the play button, this doesn’t produce spaces either.