I was doing a raid for 21w43a (yes, I know it says 1.18 Pre-Release 5, but there's not an option for that, and as far as I know, it still hasn't been fixed) and once the bar filled up, it just disappeared! No ominous horns, no victory dance from the Villagers, nothing! So I gave myself Bad Omen via cheats, and it worked! It took me a while to find the illagers, but eventually I spotted them trapped in a hole I had made! Those suckers couldn't even shoot me! So I took them out, and again, no second wave. I gave myself Bad Omen AGAIN and same thing, same place. This time, I actually went INTO the hole and realized that the pillagers weren't even TRYING to shoot me! They didn't load up their crossbows or anything! So I took them out, and pretty much same story. (I tried duplicating this in another world, but for some reason in that world, it worked just fine, and it was in the same version). I have no idea how this could happen, so I'll just label some possible factors here:

1. It was in a Desert biome, surrounded by Badlands.
2. There were Villagers with custom trades that I had spawned in using commands in the Village.
3. I was really far away from the Village when I got the Bad Omen, so I had to travel a long way to start the raid.
4. There were other Villages en-route to mine, which I avoided.

Sorry if this was too wordy, this is my first bug report. Hope this helps!