Your diamond matt topcoat needs time to cure that’s all. Durable/Scrubbable emulsions are mostly based around acrylic resins and can take up to 30 days in some instances to cure fully before being able to be wiped, cleaned down or attacked with tape for that matter ;-)
Your mist coat sounds fine if it hasn’t pulled off with the tape. Just follow the instructions on the back of the tubs of paint and you can’t go far wrong. Dusting and cleaning down the plaster prior to the mistcoat is also best practice to prevent adhesion issues.
Probably too late now but if you’ve lots more to do then I’d suggest forgetting the dulux and using crown clean extreme, little green intelligent emulsion or isomat 2000 scrubs emulsion.