Originally posted by HangarPilot:

I've seen no mention of it in the patch notes, however they did add some new events for the Mistlands so maybe the intentionally or unintentionally changed something.

I don't think it's just RNG. I've played 2 games now (new character, new world) since the Mistlands beta came out and raids seem to be happening much more often to me.

It is rng Every 45 minutes there's a 20% chance for a raid to spawn.

https://valheim.fandom.com/wiki/Events