I have 20 Dell Venue 8 Pro 5855 running Win10 LTSB and 3 different USB-C UD-ULTCDL’s . Fully updated windows and with the DisplayLink M3 drivers.
All video out to a external monitor has ceased. On any combination of the 20 tablets and the 3 UD-ULTCDL’s.
At one time they were all working. Then nothing… I have not changed or updated since I last saw them working.