@cattledog
Once again I have done a lot of experimenting both with the Delphi app and with Arduino per your latest suggestions, but I haven't been able to come up with anything conclusive.
I found another question on the forum with the same issue, and it was suggested that RTS and DTR might be the problem, so I added a capacitor between RST and GND on the Arduino but it had no noticeable effect at all.
The other question is at https://forum.arduino.cc/t/serial-port-not-reading-unless-using-ide-serial-monitor/557972, and towards the end of the discussion someone else chimes in with the same issue. The thread ends inconclusively.
Because I have spent a long time over this issue my thoughts now are to just live with it and open the Serial monitor briefly when I turn on the computer each day.
Thank you for all of your input.