HTTPS access to web gui

[redswan]

For some time now I've had problems with HTTPS access to the web GUI. Roughly once a day the interface becomes unresponsive, I assumed this was linked to the problem discussed in the Github discussion "domoticz non responsive after websocket error (#3661)".
After installing the beta, 11351, with the fix for this problem continued to have the problem of an unresponsive interface.
I did see all the extra debug messages, so it would seem the above fix was successful as Domoticz didn't crash.
Even though the interface was unresponsive Domoticz was still running as other programmed actions occurred correctly.
The only way to get the web interface back was to reboot the Rpi, restarting Domoticz was apparently not sufficient.
I then realized that Domoticz was still receiving date from some sensors I have, which communicate via HTTP and the json api.
This led me to try to access the GUI with HTTP, when with HTTPS the interface was unresponsive and without rebooting the Rpi or restarting Domoticz.
Bingo, no problems, the GUI worked fine!
Looking at the error log I noticed the following errors:

2019-11-26 11:39:05.459 Error: WebServer(SSL) startup failed on address 0.0.0.0 with port: 4043: bind: Address already in use
2019-11-26 11:39:05.459 Error: WebServer(SSL) check if no other application is using port: 4043
2019-11-26 11:39:05.462 Error: Exception starting shared server: bind: Address already in use

As far as I know no other application is using this address:port, at least not something I have knowingly started.

Apologies for this long, and maybe confusing description.

Any ideas why this situation occurs?

Chris