I restarted my computer this morning, and suddenly, the 1Password extension was no longer showing up in Safari (v12.1, MacOS 10.14.4), and so I had to re-download the application, and upgrade from there. This is not the first time this has happened and seems to happen randomly. The only thing I did yesterday out of the ordinary was empty the Safari cache on the instruction of the USPS website since I was suddenly having problems bring up payment options on their site using Safari.
But the point is is that this is not isolated behavior. It doesn't happen every day or every week, but randomly and without warning. I'm only mentioning it because it's a bit of a pain to have to re-download and the beta upgrade every time this happens. I'm not sure if the problem is on your end or Apple's.
1Password Version: 7.3 BETA-12
Extension Version: 7.2.5
OS Version: OS X 10.14.4 Mojave
Sync Type: iCloud