Hmm I’ve read a few things at https://www.reddit.com/r/arduino/comments/6b5djs/having_trouble_installing_digispark_attiny85/ and https://digistump.com/board/index.php?topic=1959.0 and their forum search in general (http://digistump.com/board/index.php?action=search2) but no conclusive answer besides try and reinstall the driver within 5 seconds, use a different USB port / cable, uninstall / reinstall driver, from some chinese clone the USB resistors / shell fell of and was defective etc. 
Since it works for me (at least the bootloader + uploading), I can’t reproduce it. You might find help in https://digistump.com/board/index.php or Issues · digistump/DigistumpArduino · GitHub.
There’s also the posibility of programming a barebones ATTiny85 with an external programmer but that then also defeats the purpose of using the Digistump. See e.g. Programming ATtiny85 IC directly through USB without Arduino using Digispark Bootloader or Tiny AVR Programmer Hookup Guide - SparkFun Learn.