@aha_1980 : I just noticed something else: In the log file, there are lines saying "GDB 71101", presumably because it is using v7.11.1 (?!). But I have installed GDB v8.2 in both usr/bin and usr/local/bin. And I've set those locations in QtCreator's options pages for kits and for debuggers. There should be no way for QtCreator to find an older GDB version.
The GDB version in both usr/ folders above is 8.2, confirmed by running via terminal. And I did not find any older stray 7.11.1 versions that QtCreator could be picking up.
Another oddity. Is there any other options page where the GDB location needs to be set?