Unfortunately i'm facing with this issue. Shortly, I bought a new pc, installed 1password 4.XX for Windows.
I tried to install related browser extensions both for Chrome and Firefox. Firefox works fine, chrome no :-(
I followed your troubleshooting as showed below but without success.
Morevover, under 1password desktop app, setting, broser plug-in, i see that chrom estension is shoed as not installed but it's :-(
Plkease can you help me?
1Password Version: 4.6.2 626
Extension Version: 126.96.36.199
OS Version: WIN 10
Sync Type: WLANSYNC