I was using Qt 5.14.2 to display local PDF files successfully using WebEngineView. (I'm on CentOS 7)

Then I updated to Qt 5.15.0 and my WebEngineView showed a blank gray screen.
Then I ran an example of WebEngineView provided by Qt 5.15.0 and I got the same blank gray screen. However I got half a dozen error messages like the following one:

"GET chrome-extension://mhjfbmdgcfjbbpaeojofohoefgiehjai/elements/viewer-error-screen.js net::ERR_FILE_NOT_FOUND"

Am I missing something?