A concluding note on this: I fixed my issue.
So, OK, my problem was fixed by simply making a clean install, and reinstalling plugins manually, rather than restoring a backup. The roots of that backup pre-date even OpenELEC before the migration to Libre, so there was a lot of cruft. FWIW, restoring the backup on a Raspberry Pi with LibreELEC 9.2.7 also causes some similar-ish hanging issues, which is what got me on the way.
Still hoping to see the WeTek core get 9.2 or 10 one day, but for the moment, everything still seems to work, including Wedevine.