2016 Challenger 700 Brake failure after Recall completed

[AJUpNorth]

I have a 2016 Cub Cadet Challenger 700 that has ~40-50 miles on it,,  and similar hours.     It had the Brake recall completed in summer of 2017 and in summer of 2018 after sitting for a month of non use the brake pedal pressure became soft and would not stop quickly as normal.   I took it to the dealer and they "fixed" it and it worked fine for the past year but again this past weekend I took it out after not using it for 5 weeks and the pedal is soft again and takes forever to stop.  I plan to call me dealer again to see if they will fix again but I am wondering if anyone else has seen this and if anyone knows what it could be.      No visible leaks and machine is not worked hard.  I use it to drive around my property.

[Travis]

air is getting in the brake system somehow.

I'd have the dealer check that all fittings or joints are screwed in tight at the master cylinder , wheel cylinders and any other joints.