They fucked up their wheel nuts over the winter break by using a new alloy, but forgetting to test it under race conditions. Turns out it expanded when hot (like during a race) and got stuck, so they had a bunch of like 20+ second pit stops in the beginning of the season, which really tanks their average.
Could you post the median values or even better visualise the distributions or give the data? Sauber had a few really bad pit stops at the beginning of the season which pulls their average down a lot, but doesn't affect the median that much.