@Vero Thanks for answering, Vero!
I just tried and it doesn't happen now... I will try to "Sample Process" next time this happens, then.
* It did happen every single time when I reported this, yesterday. I could have sworn it only happened sometimes a while ago (same machine). I have not restarted my Mac in 27 days, but I think this had happened before that 27 days. Right now I'm not in a good place to retart so maybe I can try that later.
* I first noticed it when I tried to expand in a web form, using Firefox, but I tried with TextEdit also, and it happens there too.
* I type the keyword, and it does not disappear. The content does not appear either.
* The snippet is super simple. Just my email addres. I have a short keyword for it as I have to fill out my email pretty often.