At first, it is necessary to understand that the virtual serial port is in an any way "driver" which should be "digitally signed".
> windows 10 Once
"One fine moment" presumably update 1709> 1803
MS sometimes something breaks, to treat heavily, to the mere mortal as a rule it is unreal, to press on MS probably, but too it is heavy (sometimes it is possible to force to "cure" in a year, sometimes something break so that "bug" is dragged by decades from whists to 10, and they do not correct it).
But in general, I can not confirm that in 1803 broke something globally on this subject.
And here with "signatures" there can be troubles.
It is necessary to look when also what type the signature signs the driver of your port.
After an output 10 the policy of the signature of drivers changed, but is real they it did not observe.
If it is signed to (July? 2015 date of an output 10), this one. If after, are possible .
If the reason that helps with it a mode of "switch-off of check of the signature of drivers" (F8 at start of a computer each time - for the classical menu of loading, for blue - through 2 reboots), but here how much ....
If 10 days after update 1709> 1803 did not transit, can try to roll away to 1709 (but to retain 1709 from the further attempts will "be updated" to 1803 heavily).