Choisya ternata Aztec Pearl leaf drop

I have a young Choisya ternata Aztecc Pearl.  It has suddenly had about 40% of its leaves go yellow and these are now falling. However, it is happily flowering.  Thought about it being due to recent dry spell but other plants around it, including a nearby Choisya Sundance, seem ok. Any suggestion most welcome.Thx

(I list myself as an enthusiastic amateur gardener so forgive me if I am asking obvious questions; with a young garden, I just want to get it right!)

It's slightly less hardy than the bog standard Choisya and so I suspect it may have been the victim of strong winds. Frost damage will cause die back but overall it should survive. Maybe a feed will perk it up?

Thank you. I'll give it a good feed this week as the weather turns wetter. Epsom salts for the yellowing or just a good standard feed?