I was trying to take a screenshot of Illagers celebrating at the end of a raid because it looked cool. I had already gotten a picture of a Pillager and I thought, "Hey, why don't I get a Vindicator to celebrate?" I started a raid, killed all the villagers, and the Vindicator suddenly had no arms. (BTW, there is a command block in the background of the picture that I attached. That just gives me the bad omen effect for 30 seconds because I didn't feel like killing a Pillager with a banner.)

I thought it would just raise its arms in the air and jump up and down.

Instead, it just lost it's arms and jumped up and down.

To reproduce this you just have to:

1: Go to a village with bad omen.

2: Progress through the Raid until Vindicators spawn.

3: Let the Illagers kill all the Villagers/kill all the Villagers.

4: Look at a Vindicator. Notice how it does not have arms anymore.