Hi again,
Went back to the shop today and they gave me a new one and it seems I just had bad luck with the first one; now the verbatim tests, records and formats without problems, and the whole LR16 feels more reliable and steady. We tried the power supply of my new one on the old one and it did not power up either.
Apparently my first one had a problem in the power circuit, and it was kinda half working, but the higher the load on the USB, the more erratic it would behave.
Glad I discovered this before I did an actual live recording 😉
Thanks for the help from you guys and also from the shop Olimpus who decided to replaced it immediately!

Small detail: the Verbatim 128 now records 16 tracks, but according to the test I should use 16 bit. I tried 24 bit which seems to work fine, although sometimes it gives a dropout error.