di2 is all good until it's not.
For the record, I've been riding di2 for six years and am currently on my second group set.
When my first di2 group set (2013 ultegra di2) became problematic after ~20k miles, once I rode 25 miles home with the biggest gear 54 x 28 (rear derailleur failure). Another time, I had ride through 10 miles of rolling hills with the smallest gear 34 x 11 due to another rear derailleur failure.
I had no complaints since it's over 20k miles. I went ahead and got DA R9100 di2.