Beautiful program! I'm using 4.4.1
There is a bug in the brushes lists. The program is not keeping track of the brush lists accurately.

OK - Suppose I make a new tag "Brush_New".
Then I create a new brush from an existing one, rename it, then tag it to go into a list, "Brush_New".
At that point, the program is getting the new brush confused with the previous one in the tagged list,
& the new brush exists for a while, then suddenly during a drawing session, it disappears.
I've now seen this happen several times, & the new brush exists in the "All" list, and when it is accessed
from the "All" list, I can use it, & the tag for "Brush_New" also exists on that brush, but it refuses to show
in the "Brush_New" list.

The problem doesn't seem related to the underscore character in the "Brush_New", it can happen with any name.
I'm not sure if it a known issue, but it is predictable.
I will verify that a similar problem is not there using an earlier version, & update this post if I find anything.

Further to the above, I have spent about 100 hours on the latest beta, & the same problem is still there & getting worse.
I now have multiple copies of the same brush with repeated "backups" in the name. I'm overwriting the previous
settings. When I come back next restart, everything is different. The program is not keeping track of brushes in tags
reliably. Is there a way to "copy out" such brushes & save them before I close the program? Because unless I can
keep them, there's no point in making them.

Other than that , 4.4.2 beta2 seems quite stable.

There are problems with tags and also in general with resources management.
The entire resources management system is being reworked at the moment but will not be available for release for some time.
We have to be patient about this but it will get better

Version 4.4.2-beta2 has recently been released and is more or less totally good now so you might want to have a look at it:
https://krita.org/en/item/second-beta-for-krita-4-4-2/

I suggest that you use the portable .zip package so you don't overwrite your 4.4.1 installation

The formal release of 4.4.2 on the main download website should be happening quite soon.

If you have any specific fault reports about 4.4.2-beta2 then please sign up to https://krita-artists.org/ and make your comment in a reply to this topic:
https://krita-artists.org/t/krita-4-4-2-beta-2/16136