How quickly to automations trigger? problem with bulk updates

I’ve set up a simple automation to copy data into a field when a record is updated. This works fine if you are just changing a single record but sometimes we do bulk updates (cut and past multiple records) in that table and the automation only seems to fire for the first 1 or 2 records.

Is there a delay or lag in terms automations firing, so is there a better way to handle this?