Widgets not repainting, after update() call

I have custom plotting widgets that inherit from QObject. After a call to update(), on 5.13 & 5.14 they are not repainting at all unless something else occurs, such as a mouse moving over the widget, app resize, tab switching etc.

I'm on macOS 10.15.5 with xcode 11.5.

Qt 5.12.8 and earlier and 5.15, update() triggers a repaint immediately.

I can't easily provide a repro project but from reading other bug reports, QT folks say there have been changes to the update() -> repaint logic in 5.13 and maybe 5.14.

I'd appreciate someone taking a look. I can't move to 5.15 because of other bugs in 5.15 right now.

I'm on the Qt commercial license.