Have to switch to the old UI to use the "Start Review" button on "Work In Progress" changes when you are not the owner of the change.
Noticed this has been missing from the PolyGerrit UI for a while (not sure it was ever there tbh). Only recently became an issue for us when a change owner was not available to "Start Review" on their WIP change.
We're running 2.15.3-4891-gd3b6904d9d (updated this morning to check before posting!).
Thanks,
David.