I had a raid trigger without warning on my 1.14.3 server (Normal difficulty) last night. While trading with my villagers, I noticed a patrol just outside the village, grabbed a milk bucket, and was hoping to lead it away to kill them and secure the border, but instead it triggered a full 7-wave raid as soon as the patrol noticed me. I had not yet interacted with members of the patrol and did not have the Bad Omen effect. My entire village was slaughtered.
Can confirm. I had 7 waves with vindicator-ravager riders and everything on Normal difficulty. I didn't have Bad Omen at the time it started, so that's probably a separate bug.
This issue is much worse when leaves are decaying.