Strawberry leaves issue

Hi, I'm new to the forum and am having trouble identifying a possible problem with my strawberry plant.
I've attached a picture of its leaves, which are turning brown, but in the middle. The outer part of the leaves has lost its glossy characteristic, while the inner part, outlined by a brown line, remains green and glossy. I have looked up chlorosis through overwatering and it doesn't appear to be that (no dark green veins etc.). Any help would be much appreciated. The new leaves are growing green and healthy and the plant is producing both flowers and strawberries. However these affected leaves are not from last year and are relatively new leaves. Some of my strawberries are growing really well but others stay small, change colour early and are quite solid and dry inside.
Thanks for your help and advice.

 

Hello Hiplm and welcome to the forum.
I can't see the pic of the leaves too well but strawberries can be quite prone to botritis. Have a google for that and see if it is the problem.

 

Doesn't look like botrytis to me. There's no rotting going on at all. Anyone got any other suggestions?