Brake lever adjustment causing sponginess?!

Never had this happen before but when I adjust my levers to be closer to the bars so I can reach easier they become really spongy. When I move them further away they firm right up again.

Anyone any ideas why this maybe happening?

They’re Shimano SLX m666 if that makes any difference?

Quite baffled!

Cheers

Happens on my xt and xtr brakes. There’s a tipping point on the reach adjuster. Beyond that point they go spongy.