Progress...

Don't want to jump the gun here, but I think I may have done it.

Just ran the Museum of Technology quest with FIVE companions in tow, and not a single hitch.

No, I didn't cheat, and use others from another system. These were all RR.

Had the one stoppage that always occurs. I don't count it. The game is coded to stop companions from accompanying you into the elevator, and up into the Washington Monument. Forcing them to stop following the player has the predictable side-effect of making them default to whatever else they do. Vanilla followers stop and stand there, RR companions default to a sandbox.

A group order to follow brought the whole merry band back into line, and we continued off.

No hesitations, no stopping, no delays in following me through cell-change doors... I think I may have finally done it...