App not sending client certificate

[sasbibic]

Actual behaviour

At first start all works ok, leaving app in background for a while and then reopen it, app fails to authenticate with provided client certificate
Displays error from nginx:

400 Bad Request
No required SSL certificate was sent

Expected behaviour

Should provide certificate all the time.

openHAB Server log

Click to expand

Not required.
If you have installed openHAB via `apt-get`, the log is located under `/var/log/openhab2/openhab.log`