Tried raiding Abaddon earlier. Launched the raid with 2 people. Get a message saying

Tested raiding a normal boss and that went fine.

Just thought I'd log it

In addition to this, I seem to get the same message whever I raid a rival guild. No joy raiding other guilds so far!

Do these guilds have zero power, meaning they have no active (in last 72h) players in guild? That would be why.

Is that a thing now? Thought there were no restrictions on raiding.

Nah, that issue has always been around.