I’ve used many different
I’ve used many different types of USB tuners over the years and this was a very common problem with just about all of them. Sometimes the problem stemmed from a flaky USB hub, a bad connection, or bad cable. If you’re connected directly to a USB port on the PC, try a different port. If that doesn’t work, try a different cable.
I’ve got two internal InfiniTV4 tuners but never tried the USB version. If it does not have an external power supply and only uses the USB port to provide power you may want to try using an external powered hub. It’s possible the tuner is putting too much of a load on the internal USB port. You might also want to try some contact cleaner on the USB connection. Dirty contacts make for a bad or intermittent connection which could be causing your tuners to drop off line.