Hey Ben!
I have experienced the same issue and actually, I was just able to solve it...
My situation: Enpass Safari Extension Connection Error
I had a 2015 MacBook Pro running with macOS High Sierra. Enpass used to work fine with all browsers (Safari, Firefox, Chrome)
A couple of weeks ago I switched to a 2017 MacBook Pro via Migration Assistant. On my new MBP, Enpass still worked with Firefox and Chrome, but did not work with Safari!
Always displayed this dumb connection error...
Now here's what I did:
Uninstall and re-install Enpass for macOS (tried both the App-Store and the Enpass-Website versions)
Uninstall and re-install Enpass Safari Extension (tried both the Safari Extensions Gallery and the Enpass Website versions)
Install Enpass for macOS and Enpass Safari Extension DEBUG versions sent to me from Enpass support
And all of this didn't change a thing!
Here's what solved my issue:
After reinstalling Enpass and the respective safari extension about a million times, I decided to re-install macOS without erasing my data.
A reinstallation of macOS is the only way to re-install Safari.
How I did this:
Make a Time Machine backup to an external HDD or NAS.
Go to Mac App Store, search for High Sierra and download it (around 5 GB)
When the download is finished, the High Sierra Installer pops up
Simply re-install macOS this way (this does not affect your data!)
-> and then be happy things are working well again!
And - voilà - this solved the problem for me.
Now everything is working well!
Good luck,
Oliver