Hi RachelW,
The latest fix around USB redirection issues in combination with DEM/UEM shipped in Horizon agent 7.6, supported by a change in UEM 9.5.
There's an ongoing issue that seems to be triggered by "slow" logons, where the Horizon agent can't determine the session ID within its default timeout of 60 seconds. Kjell's post earlier in this thread lists the Horizon log message to check for ("Can't get a valid sessionId within 60 seconds for channel") and the workaround (overriding the timeout by configuring the WaitForSessionIdTimeout registry value.)
However... If you have the UEMFlags registry value configured, you should not be encountering this particular issue. That value instructs the Horizon agent not to look for Horizon Smart Policy configuration provided by DEM/UEM, so it won't try to determine the session ID which it would have needed to do so...
Probably best to open up a support case, so VMware support can take a look at what's going on.