I have serious issues with Cosmic. When I lock the screen and come back, then it has kills all terminals except the Cosmic terminal, firefox has become... broken, for the lack of a better word, where all new pages just give gray background color and no menu items work, and the sound is reset to the laptop speaker instead of hdmi, not the disolay though, only sound. Then fullscreening terminals also makes them crash, as in they seem to refuse to take input.
It is not really usable. But since nvidia on x11 in popos started resetting the display config when the screen went to sleep, it beats the alternative.