VASSAL not recognizing my player side choice

Model: MacBook Pro (Retina, 13-inch, Mid 2014)
OS: macOS Mojave 10.14.2
CPU: 2.8 GHz Intel Core i5
Memory: 8 GB
Video: Intel Iris 1536 MB
VASSAL: 3.2.17
Java: 1.8.0_201-b09
Module: Terraforming Mars A-2.1 … rs_21.vmod

While trying to debug a separate problem with loading games, I reinstalled VASSAL, which caused my module library to be lost, so I had to re-add my modules. I can now load games, but I am prompted to pick a side, and the side I’d previously chosen (Yellow) is not in the dropdown menu. I am not asked for my name and password, though they are stored in the module preferences (Personal tab).

If I have the same name and password as before, should the module automatically recognize me as Yellow? Am I supposed to be prompted for my name and password? Is there a way for the other players to somehow retire Yellow so that I can join?

This is a classic symptom of your password NOT being the same as it was before.

Do I need to run the module, load the game, join as an observer, change my password in the Preferences, then quit the module and reload the game?

Yup, that did the trick.