dura ace brake hydro issues

[Bmctmr01]

Cant for the life of me find anything on this maybe I am a little stupid.

SL6 with dura ace hydro di2 on and have nothing but issues with the rear leaver not working..had a new one replaced in Mallorca last year and now this one has got the same issue.
the leaver just pulled all the was to the bars nothing happens and then it sticks. I have now moved to mainland spain and was told from the bike shop here that they don't like to get hot, big issue I I lived on Mallorca and now mainland spain where the temp is 30+ in thee summer.

Anyone else have this issue?

[timmerrr]

Contaminated master cylinder. Waranty it. I had to do both of my levers on my S5 with in a year of buying it. Pretty common issues with no real solution, just a crap shoot as to whether it happens or not.