serial test on UNO & Mega works, on UNO Wifi Rev2 not

the sketch is just a Serial.println("test") every 2 secs.
on my laptop Windows 10 i open the port (in a Puredata patch) and wait for what comes.
with an UNO & Mega the text appears as it should.
with the UNO Wifi Rev2 the port is opened but nothing comes through.

continuing with the Rev2:
closing the port in the Puredata patch, opening the serial monitor of the IDE, the text comes through.
after closing the serial monitor and opening the port again in Puredata "test' finally appears.

i've been working for years with the regular UNO and never had this problem.

rolf

found with the help of the Puredata forum:

sending a DTR 1 to the port got it working.

with the 'regular' UNO DTR 0 or 1 doesn't influence the communication.

rolf