Thunderbird doesn't update

I posted this to the Thunderbird forum thinking it is probably a Thunderbird issue. They suggested I post here, so here goes. I've had Thunderbird installed as a "Portable" application on my Thinkpad X1 (6th gen), Windows 10 Pro machine for over a year (installed on 06 Sep 2018). Profile resides on a network location. Never had a problem with Thunderbird updates until I noticed an issue today (it looks like the last update, v60.9.1, was on 07 Nov 2019). The update presently fails for an "unknown reason". I've tried the suggestions in another Thunderbird post multiple times but no luck. I also have Thunderbird portable installed on another Thinkpad X1 (4th gen), Windows 8.1 Pro with my wife's profile also on the network. That Thunderbird has been updated to 68.3.0 (installed on 06 Dec 2019).

When I look at the Portable Apps site they only have v60.9.1 so I can't seem to upgrade that way because I'm there already. Any additional ideas would be appreciated.