It was on a google site somewhere just saying they were aware and
working on it. It may well be that Covid etc has delayed any fix. I am
not sure about Chromecast as I rarely use it. I have Google Speakers n
every room and a paired speaker in bedroom...
I saw a note to say they were aware of the problem and would fix it.
Since then I have had no problems. But they would roll the fix out in
small portions just to make sure nothing else goes wrong. I am in New
Zealand so maybe I got it first not sure.
I think it has been fixed as it no longer does that. It might be worth
turning off the pair and then turn them on again and see if that helps.
I always have my phone handy and at the worst you can use the Home app
to change the volume.