1Password for Safari not responding
I have the same issue with Safari: neither Autofill (from the 1P icon in the Safari ToolBar) nor the small icon from the "1Password for Safari" extension in the username/pwd login fields work reliably for autofill. The issue came (also for me) up with Sequoia 15.4. I am using the most recent versions of 1P (81072027, no new Beta yet), Safari (20621.1.15.11.10) and 1P for Safari (8.10.70 - no new version in the App Store yet).
There are various reports about "intermittent" failures, my impression is that there is a serious issue with 15.4. (as pointed out above).
Michael_Shingledecker and bwadm
It sounds like you're both running into a known issue where 1Password's suggestion menu will stop working, and Autofill will stop filling. Our developers have identified an issue in Safari 18.4 that is involved with this behavior and we're working with our friends at Apple to get it resolved.
For the time being, opening the website in a new tab should get things working again. If that doesn't work then restart Safari by completely closing it and then reopening it.
-Dave