After the alleged software fix for my steering issue in January, in mid February the problem re-surfaced as badly as it had initially in October. Once again, steering assist was extremely erratic, ranging from none to suddenly seeming to want to put my car in the next lane on its own. Called the dealership and BMW Customer Service again. The car had developed another minor issue: at times, pressing the brake pedal and the Start button, which should put the car in what BMW calls "Drive-Ready State" would only initiate "Radio-Ready State," which is similar to the Accessory position on an old-style ignition that requires insertion of a key. It turns out this is related, and my car is in the dealership's shop now awaiting the arrival of a new EME module. Interestingly, this module is the subject of an actual recall on 2018-2019 MY i3s.

Anyway, when I brought it back to the dealership, the steering was again better, but still not "normal" - still had the "sticky" feeling and lacked self-centering again, just as before. The EME module replacement is an extensive repair, requiring removal of the electric motor, and it will be another week before I get my i3 back. I am hopeful this will finally fix the issue, but am currently not enjoying the BMW experience overall.

Update from Nov 23, 2021: In October 2020, I got another dealer Service Department involved. They observed that the bushings at the tops of the front strut towers were different thicknesses (passenger side was thinner than driver side), so they replaced both and aligned the steering. This had no effect on the issue. When I brought the car back again, they replaced the steering rack. It's now over a year later (late November 2021) and the issue has not recurred, so that seems to have been the fix.