As far as I have no problems with all other Ubiquiti devices then every USG-PRO-4 I got in touch with, was causing problems. One client couldn't use it with its ISP, the USG-PRO-4 couldn't connect to the internet at all. Another client had 2 external IPs, USG-PRO-4 could work with only one of them and it was disconnecting randomly. Every adaptation took 30-40 mins and it was usually failing. Support said it's a faulty device and sent a replacement. The replacement was working in exactly the same way.
USG that I had at home, was disconnecting randomly and I had enough of it after a couple of days.