Since a couple of alpha builds the random disconnect while/after a manual scan was solved for me.

Same

So if I just scroll all items on AH manually without pressing scan button addon will get all new prices? Because it's simpler and faster and without disconnects than pressing the button.

That does work. Although, fingers crossed, the latest alpha on discord fixes the issue.

As the original poster no longer has the issue, closing

It's disconnects even with 200 (250 was default)

Beyond "use the slow scan mode" we don't have any good solutions at the moment. We did speak to a dev about making the "fast scan" work, but making the changes they suggested to our code would have resulted in a 8 hour (not a typo) scan in some cases.

8.3.0.7 still disconnects

Can you try Shift+Clicking the scan button - it does the scan in a slower way that's less likely to disconnect

It's ok, but it's super slow, I can scroll all items manually faster

You could try reducing the full scan step size in advanced settings - lower values can help with disconnects