I use the spacebar to pause/unpause Infuse on my Smart keyboard quite a lot and noticed that it sometimes stops responding. The only way to get it back working is to force quit the app and start it again. The keyboard just works fine after restarting the app. I also tested it outside of Infuse when it stops functioning and it works fine in other apps.
Running iPadOS 13.3 on a 3rd gen 12.9 iPad Pro.