@mitsuki48 iirc, it wasn't Umino who mentioned that she had been dealing with anxiety and depression issues, but one of the professional shogi players/consultants that do their columns in the tankoubon releases of the manga, as they confessed it in one of those.
Either way, about the shortness of the chapters themselves... it's a bit tricky to think "they have been decreasing a lot as of lately", because even in the more recent chapters they tend to vary from 14 pages to 10 pages long (I'm including the covers, and the chances of there being double pages).
I wouldn't doubt that health issues (physical and/or mental) might be influencing in making some of them shorter than others, but I'm also not sure if Umino is working by herself or if she has assistants around, so it may be affecting in the length of the chapters themselves, too. (Other thing to consider is that we don't know if the pandemic could be affecting some of her work process, too, regardless of how Japan seems to be handling it as they have returned to a "normalcy" degree right now).