Problem with Wemos using ch340

[djmGH01]

I tried to use a Wemos Mini (Banggood) in combination with a ZIV smart meter.
The WeMos did go offline after initiating startup.
Checking the signal on the transistor collector (connected to rx) I noticed it is not getting the proper "low" signal.
In this, I did not connect to the ZIV meter, but checked the TX line at the RJ12 connector as being "high" (i.e. pulled high to 5V).
Is this failing signal value a known issue due to sharing the rx input with the CH340 line?
If so, is there a solution to this?
Looking forward to any reply.