Hope M4 brake and in the wet especially it gets a bit stiffer to use although in the dry its not that noticeable.

Any ideas where to start on this one?

I can ride with it but its one of those things i wouldn’t mind sorting out.

Also while i’m at it, rode in the alps this weekend and the brakes took a right battering. flew back home with plastic spacers between the pads and now both brakes feel like they’ve lost oil or something. the lever goes all the way to the bar without doing much.
Going to bleed them to hopefully clear the problem but why has this happened?