killall or
pkill terminates processes by name. It's not a solution on it's own, but here is a brute-force approach that will terminate Safari and 1Password things
for all users of the system.
Stop 1P background/service/daemon/helper processes
sudo launchctl stop *com.agilebits.onepassword*
Stop Safari, unload 1P Safari extension, helper process, desktop app, 1P mini?
sudo pkill Safari 1Pass* com.agilebits
Once all 1P things are stopped, the update should go through. If it's still not working, check to see if there are other 1P processes that are running or have just restarted
List 1P background/service/daemon/helper processes
sudo launchctl list | grep *com.agilebits.onepassword*