Could it be frost damage?

This looks like 'burn' to me. Either from an ice episode or, less probably, from very hot dry wind and strong sun. Second explanation, some sort of salt damage maybe from wrongly applied fertilizer. I've also seen this happening when a pet decides to use a plant as a toilet...
Nik

I would guess a mistake with fertilizer. Flush out the soil with extra water.

Maybe Ambridge does not like either the fish emulsion or getting it on its leaves?

My Ambridge had similar thoughts on it, only plant that did not like the foliage feeding

Ambridge Rose was terribly fussy here. I felt badly about that, but its foliage was always complaining about something or another, and much of the time, it rusted.

Jeri

I don't know how cold you've been but that does look like frost damage to me. Every rose is different and some are more tender than others so don't try to compare them with each other or you'll drive yourself nuts. Just observe each one and learn what they like as individuals.