A change can stop before every row is written. The result page says "Applying these changes stopped partway" and lists what was done.
What was written stays written
Every row marked Updated was written and read back. Rows marked Not updated were not reached. Nothing is half-written: a row is written in one go or not at all.
Carry on
The page offers Carry on, which writes the rows that were not reached. It is offered until the change is reverted, or until a newer change of the same kind of row is applied.
Stopped before anything was updated
"Applying these changes stopped before anything was updated" means the app was still reading your store when it stopped. Nothing was written. The page leads back to Review changes, where your drafts still are. Press Apply again.
Some rows could not be updated
When every row was reached and some failed, each Failed cell shows Shopify's reason. Fix the value in the grid and apply again; the Updated rows need nothing more.