Don’t know. Never had a replacement card from Monzo before (aside from when prepay card was replaced with proper bank card). But chat support has advised to destroy and discard the old card when the new one arrives.
Fair - my bad
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You’d have to live with that “activate your card” banner in the app forever and hope that, while monzo have forgotten that you didn’t get a new holographic card and forced you to have a new hot coral card, they’ve also remembered that you didn’t get a holographic card and aren’t about to cancel your old card 
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This and you can’t see your “contactless until C&P” limit. I’m living with this on my JA at the moment.