This might help others. FYI, yesterday I upgraded to the new 3.9.8 version of DEVONthink. I soon found out that PDF’s “printed” by DEVONthink were not opening in the app “PDF Squeezer”. I rely on “PDF Squeezer” to make huge space savings.
I have no idea why, but re-booting the machines (iMac and MacBook, both with current macOS versions) resolved the problem.
@BlueFrog often recommends a re-boot to help solve problems.