Rambing rose not rambling

Hi

i'm trying to grow various rambling roses up old Leylandi stumps on a east facing side of the garden.  Two roses have really taken off but tge Super Excelsa rose is very poor and the leaves are small and mildewy.  No rose hips either.

All are in the same position, planted at he same time two years ago.  Any ideas what could be affecting my rose?  pics attached showing comparison between good ones and the bad one ... then a close up of the bad one.

Any help appreciated.

Susan