The theme I'm using is "StimuWrite Two" with a custom background, and I'm using the Yellow Heart emoji.
From my use over the last 2 weeks, it seems that it crashes when the app is open for too long, like for a few hours. So if I were to leave the app open on my machine for an hour or two and then I come back and type for a while it crashes. Another thing that I've noticed particularly on my laptop is that it starts to heat up if StimuWrite is open for over an hour, and it starts to cool down minutes after I close it.