My client didn't get a deadline reminder

Reminders only go to client accounts on the project, on the days you ticked, from 9am UK time. Here is what to check.

Check they are listed under Client accounts in the project’s Settings, with their invite accepted. Reminders only go to client accounts: not to guests who comment by name, and not to someone whose invite is still waiting. If there is nobody to remind, the Feedback deadline section says so.
Check the nudge days ticked under Feedback deadline. A nudge only goes on those days, from 9am UK time.
After the deadline, chasers only go if Chase is set to something other than Don’t chase, up to the Stop after limit. They stop once your client leaves a comment or reply on or after the deadline day.
Ask them to look in their spam or promotions folder. To see what the email looks like, press Send me a test under Client reminder emails in Account & notifications.