Scrollbar issues on macOS

One more issue, after just upgrading to 2.8.12. The scrollbar on an iMac running macOS 10.14.3 is very erratic. It displays as small when first loaded but then jumps around to very large, then back to small, then back to large again (without user interaction). Clicking on a term actually selects the term above or below it and then the scrollbar starts jumping around again.

Sorry to be high maintenance but I have a release deadline looming and I'm trying to get everything finished on time.