This hasn't ever happened to me previously and I edit hundreds of images a day, as a wedding photographer. Has only appeared since latest update (so far as I've seen).
Edit an image in Develop mode, normally the thumbnail at the bottom would auto update with the new preview/look. It doesn't anymore. Go to Library mode to check, no, no update to the preview, it's still the old look. Force rebuild standard preview (and 1:1 preview) no effect. The Library preview will not update to the new look created in Develop mode.
Quit LR, then restart it, the preview is updated.
Even did a Sync of one process, which was converting to BW across 5 images. Four of the images changed profile to the new look, the 1st image in the group didn't. Stuck with previous old version of the look. Quit and restart LR it changed to new look.