Well, I tried deleting one of the things altogether and adding it back in. Removed it from the z-wave controller, deleted the thing, re-added. But still behaving the same way.
However, I then did a little more experimenting with the dimmers. If I just tap them to turn them completely on or off, they will not update in OH. If I dim the lights with the switch, to any percentage, they will update! It’s just a full-on or full-off (from any percentage) that does not update in OH.