The baud rate on the console is set to 115200 as is the baud rate for Serial.begin(). In the process of loading the application (Read Serial) the downloader sets the baud rate to 430400. I don't know where the 921600 would come from.
I tried changing the default Windows port setting from 9600 to 115200, but noticed no change - still fails with same error messages. I also verified that the latest ch340 driver is installed (3.5.2019.1).
The current circuit is nothing but a Wemos D1 Mini connected to the USB port.
I tried uninstalling the latest windows update and i get an error "This action is only valid for products that are currently installed"!
I'll keep working on it.
Dan