Yesterday I created a couple of test projects using 4.25.1. I clicked on Launch, and all of them were launched without problems.
Today, however, I opened the same test projects and clicked on Launch, but this time, every time, Unreal Engine froze. I tried using a new, blank project. Same result.
Uninstalled and Reinstalled. Same thing.
Installed 4.24.3 and tried with a new, blank project. This time it worked.
I am reinstalling 4.25.1 after deleting some files still in the system. Will comeback and report if that did the trick.