Double hung exterior doors

Hi All, I have a shed with double hung doors, I'll try to explain what's happening,the jambs are plumb the doors are plumb,bottom of right side door on both the jamb side and latch side seem to have swelled making the doors hard to close, both edges have what appears to be a piece of thin pine for weatherstripping,I have tried to plane it,it helped for awhile,but I need a better solution.

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