I had to reflash my Xperia X for 4.4 after an upgrading issue.
It now seems that USB modes are gone. I don’t know in which version this last worked as I haven’t used MTP for quite some time.
I tried 3 different cables, they all charge but none of them work for MTP (or USB IP connection).
It may be my physical USB port, this thing is almost 5 years old by now.
Is anyone else seeing this problem?