Some days ago I send my laptop to sleep and there is a black screen with cursor after wakeing up. BUT if you turning off it with power button everithing is fine. I have tried all solutions finded in the Net and nothing helped. None of buttons or hot keys works except the power button. Ok. Last attemt was reinstallation all Kubuntu and the problem is saved. I really need help because the laptop without sleeping mode is useless stuff.
I use ACER Aspire 3 A315-21 laptop with Kubuntu 18.04 KDE Plasma Version is 5.12.8 KDE Frameworks Version is 5.44.0 Qt Version is 5.9.9 Kernel version is 5.0.0-23-generic

P.S. I guess the problem with some upgrades of OS because there were no any problem until yesterday and it is saved even after reinstallation.

Did you upgrade to Kubuntu 18.04.3?

I always just upgrade all which are suggested. That is why I don't know the status of my OS at that time.
But now I am at Kubuntu 18.04.3.

Right, just wanted to make sure. The problem is that you need to take this to the Kubuntu developers directly through a bug report, as current Plasma is much more advanced. The LTS support is done by them, not by the KDE developers. I am on Kubuntu 19.04 with Plasma 5.16.4 and don't have such a problem, my laptop wakes without problems.

Your other option would be to use a more recent Kubuntu version, dropping the LTS one.