I used the https://github.com/husisusi/officeonlin-install.sh script to install everything needed on Ubuntu 16.04. Used the latest Apache reverse proxy config and SSL certificate with Letsencrypt. I can open the admin panel, but when I try to open a test document: https://office.mydomain.com/loleaflet/myID/loleaflet.html?file_path=file:///opt/online/test/data/hello-world.odt, I get this error message.
I have found these two errors in the loolwsd.log:
wsd-10027-10387 13:02:37.173932 [ docbroker_018 ] ERR Invalid or unknown session  to remove.| wsd/DocumentBroker.cpp:1067
wsd-10027-10387 13:02:37.173939 [ docbroker_018 ] ERR No socket associated with WebSocketHandler 0x0x7f144c00f350| ./net/WebSocketHandler.hpp:100
Any help appreciated!