In the new FAQ, the text for massive reads, "After a Massive figure ends its movement in spaces containing at least one other figure during an activation, Start of Round, or End of Round, the Massive figure cannot move any more during that activation, Start of Round, or End of Round." Given that this text doesn't use the word "respectively" or another equivalent to imply that it applies to each separately, does this mean that if you end your movement during one of these phases, you cannot move again during any of the other phases this round?

For example, if a Bantha Rider figure ends its turn in an opponent's square, does it forgo movement points (but not the attack) from playing Jundland Terror?

I think if it meant for the rest of the round it would say "...this round" rather than the wording they used - "... that activation, Start of round, or End of round."

Given previous ability rulings I would think the word "that" should prevent each from affecting the others. Sorry I don't have any examples in front of me.

A massive figure can end movement on top of figures once during each activation, once per end of round, and once per start of round.

Ending movement on top of figures does nothing to the remaining movement points, they just cannot be spent to move the figure anymore during that activation, that end of round, or that start of round. (Nor can use other ways to move the figure.)

That was how I've always played it, but I wanted to verify that it hadn't been changed.

How does the general rule work with Beast Tamer? Can I land Bantha on an opposing figure during BeastTamer, use stampede, and then use stampede again during my regular movement during my activation?

No. Beast Tamer movement points are spend during the activation.

I read it the same. Once during each of listed phases.