I use standard settings to open Mission Control in MacOS Mojave 10.14.4 on MacBook Pro.
Normally swipe up with 3 fingers move all windows into Mission Control mode and I can switch to any available window.
After some time period of time (may be several days) Mission Control stops working.
Swipe up gesture freezes my Mac for about one minute (only mouse cursor can be moved, no other changes on screen). After one minute (without any error messages) I can use apps again, Dock works as well, Cmd-Tab works to switch between applications, but Mission Control doesn't appear in any way. I cannot start it neither by using Shift-Up (standard shortcut), nor from Spotlight.
There are a lot of 'solutions' in internet, where everybody advise to restart the Dock. I have restarted Dock several times, both using Activity Monitor, or Terminal. Dock process Id gets updated (it seems to be restarting), however it doesn't solve my problem.
Only workaround I found so far, is to reboot my Mac. However, I'd like to avoid any rebooting if possible.
Best Answer
The solution/workaround so far. Thanks to Shaded, who posted a comment with this workaround.
TL;DR
To unfreeze Mission Control without restarting MacBook
Details
It seems, that the problem is caused by some configuration issues when MacBook works with an external monitor. After disconnecting the monitor, a display driver(?) is being reset(?), Mission Control doesn't freeze anymore, and monitor can be connected again.
Important note: The MacBook should go to standby mode (sleep) after disconnecting monitor. There is a 'Sleep' item in the Mac system menu. I didn't test if it works. I have just closed a lid and went to drink a coffee.
Another note: At the moment of freezing - CPU load is 100%. MacBook is getting hot and turns cooling fans at maximum speed.