If you've boldly gone into the world of Win 10 1903, and you've already dealt with any ACP auto-repair and MaxIm repair, one more thing to check.
One of my serial ports failed to work - turns out that Win 10 1903 feature update turns ON Serial Enumeration again, to look for MS Serial Mouse. DUMB. It should respect existing settings.

Fire up the Device Manager:
Start... Run devmgmt.msc

Look at all your COM ports.

For all your FTDIchip (and possibly other) USB/Serial devices, focusers, cloud sensors, dome controllers, etc, check the Advanced Settings for the FTDIchip drivers.
Turn OFF:
[] Serial Enumeration
[] Enable Selective Suspend

You might turn on:
[x] Disable modem control at startup

For other brands of serial devices, make sure this is OFF:
[] Allow the computer to turn off this device to save power

Also, check if there is a MS Serial Mouse (that probably should NOT be there these days) under the HID / mouse section.
Disable that device.

The good news is this upgrade left the FTDIchip drivers alone; they stayed current unlike the last time.

On another machine, it did remove nvidia video card drivers and intel drivers. Both were easily fixed, although it was annoying.