I think the UK is in the same situation as Australia (where I am). The Model 3 production for Australia - and (?all?) other right-hand-drive countries - switched to China, and the factory there isn't making Performance ones yet, only SR+ and Long Range. Your order may have just missed out on getting a car allocated from the last right hand drive performance build run in the USA factory.
As far as I know, Australia isn't getting any Performance Model 3s until June-ish (and they will be made-in-China ones), so that likely fits in with the delivery time you are being told too. The recent big delivery of SR+ and LR cars in the UK and Australia from the China factory happened around the same time, so maybe next quarter will be the same.