[2020] Honorary Crewmate is a bit much

Trying to get the Honorary Crewmate achievement in a group effort, there seemed to be something we were missing.

During the event defending the ship supplies from the White Mantle, occasionally a Mesmer would spawn, teleport to the supply stack, and port back in seconds, costing us the achievement.

Seeing as they all had strong defiance bars, it seems impossible to accomplish, and 1 AP for this looks like a teaser from the developers.

Any tips or similar experiences? Scaling also seems a bit off, with champs or elites spawning at rather low player counts, or not spawning at high player counts.