Hello, theRat, thank you!

Yes, the latest version of the program is installed.
I don't think my code is very large - about 25,000 lines and no more than 1 MB in size
If this is a buffering issue, I want to see an error message anyway!

I don't have any more ideas. I will change the PC and power supplies.
I can replace the controller or put a program to monitoring of usb port and see what happens there... but it takes time and I don't have it!

(I'm sorry, there is another machine nearby that works non-stop for 2 years. LinuxCNC, LPT port, low-cost old PC, low-cost motors and drivers TB6600...
I assembled an expensive machine with feedback motors, with good hardware and software and... And I have machine stops several times a day!)