Did you check the combat log? It should show the rolls (which are made with advantage because you're paralyzed) and the hit calculations.
I did not, but even when rolls against an AC of 30 are made with advantage, the chance to hit me 4 times in a row (even with advantage) are so low that it's unlikely and probably didn't influence this.
Also, nowhere in the Hold Person description does it state you can now hit those under influence of Hold Person with advantage.
Like people said Hold person is WIS save or get paralyzed. While you are parylized attacks against you have advantage. You can check the combat-logs to see what the exact dice rolls are.
Depending on what level the fighters are its easily possible that they have a +8 or even +9 to hit (+3 to hit from prociency, +1 from weapon (which most Githyanki seem to have?) +4 or +5 depending on STR).
Your AC isent 30 however. You say the Fighter made the 3 clones himself, correct? Because mirror image only works on the caster. If you are stunned (hold person) you stop conentrating on your spell. So your AC is back to 21.
