Automation glitch?

When I’m adding automation to (for example) volume, the draw tool sometimes works, other times doesn’t. I can see no pattern. Except it’s doing this a lot. I’m using Windows 11 with Cubase 12 (just upgraded) and never experienced this problem once using Cubase 7. Sometimes I’ll click the automation pen several times, with no result, then seconds later those clicks materialise as automation points. This is very frustrating. (Won’t report it as a bug until I’m sure it’s not me). I have write enabled, track is not locked. And, as I’ve said, I think it’s a glitch because it doesn’t work, then, seconds later (or sometimes longer), it works and I’ve changed nothing.