Thanks Anshu. It works in Firefox and Safari.
I tried uninstalling and re-installing the Enpass app, and also the Chrome extension. Still the same.
Enpass Helper is running, and the lsof output is:-
COMMAND PID USER FD TYPE DEVICE SIZE/OFF NODE NAME
Enpass 2672 joheller 26u IPv4 0x23d5fe3e5d102cbb 0t0 TCP localhost:10391 (LISTEN)
Enpass 2672 joheller 28u IPv4 0x23d5fe3e5d10109b 0t0 TCP localhost:10391->localhost:52212 (ESTABLISHED)
EnpassHel 2687 joheller 9u IPv4 0x23d5fe3e5d10073b 0t0 TCP localhost:52212->localhost:10391 (ESTABLISHED)
I used wireshark to capture traffic on port 10391 on the loopback interface, and it appears to show the websocket being closed by the extension soon after it is established. I'll send the packet capture to support.