Re-installed the game using the download files, lowest resolution. All was working fine. Mission 1, no issues. Mission 2, no issues.

Search for the Nonnah, every probe droid, every friendly rogue, every tie is just jerking around. Not stable, predictable flight paths just jinking in an uncontrollable manner. How do I correct this?

The game designers did a no-no and assumed CPU clocks would stay constant, so make them constant.

One way is to go in your BIOS and lock your CPU cores to a given clock speed, or grab an overclocking tool (AMD Ryzen Master, Intel XTU) and make them constant. Since you're running a game designed for Pentium 1, you don't have to push your CPU very hard at all.

One way is to peg enough of your cores at full load that they reach a stable clock speed and stay there (see: folding@home)

Also restart the game if it starts doing that again.

... It still doesn't feel right.