Why does ubuntu (mate) freeze?

Question

linux

I put the mate environment on top of a freshly installed ubuntu.
I started irregularly (yesterday and today), the interface freezes in light tasks (yesterday, when Steam downloaded the game, today - when I coded in the atom, with YouTube in the background).
The sound continued to work, but the system reacted only to ctrl-alt-delete (I didn’t guess to try to exit the cs mode through c + a + F1) - the mate loading screen (with dots) appeared and the system calmly went into reboot.