Command Shift 5 capture of portions of the screen broken

Suddenly I am finding that if I use this command sequence I sometimes go to capture the highlighted area and it doesn't produce the capture sign. I do it again and get the sound but then the area I have selected for the capture remains on my screen highlighted, but everything else of any kind is grayed and I cannot make the highlighted panel disappear without rebooting. I am using Sequoia 15.3.1 on iMac