In addition to starting this thread, I emailed Enpass about the problem and this is the response I got:
"We have released the Enpass v6 for all the supported platforms and sorry to say but we are not releasing it for Windows Phone. As you know, we have rewritten Enpass 6 on all evolving platforms from scratch and we didn't find the Windows phone app promising enough to consider where Microsoft itself is not releasing any new updates and no new phones are coming. Also, recently, Microsoft itself said "With the Windows 10 Mobile OS end of support, we recommend that customers move to a supported Android or iOS device..."
I replied that whilst we all understand that Microsoft are ending support for Windows mobile 10 at the end of 2019, the difference is that Microsoft has given users plenty of notice to make alternative arrangements in good time, unlike Enpass which has unilaterally removed support for Windows mobile 10 with no notice and no announcement, leaving their paid up users to find out themselves when a password they have changed on another device is not updated on their Windows Phones and visa-versa.
I've since had no further reply.