Have not been able to reproduce this, but it was a significant enough performance issue to send a report. Might be related to: https://bugs.mojang.com/browse/MC-157697 

Started a raid with two players in two different villages. Players went underground to hide from the Pillagers. After the wave started, there was a noticeable TPS drop. Could not find all of the Pillagers in either Village after resurfacing. Have attached the related debug reports.

This was on 1.15 pre-3, but since I can't select that in the dropdown, and I can't reproduce, I put it to pre-7.