Slitherine

You start out the game with 3 campaign objectives.
1. Learn the Lost Cause spell
2. Be at least an Average Power
3. Be at peace with all realms

Not sure if this should be a bug, but I was allowed to declare war without getting any kind of problems due to objective 3.

Anyway now to the actual "bug" that I found.
Without having competed the 3 objectives I got a 4th.
4. Own at least 5 landmarks
Which I instantly completed due to having conquered Evengaad, Odenheim and Myrmont (Lagenwerp has Craddle of Science)

Objective 3: this is not a bug. You can go to war or be at peace at any time. However while you are at peace, you will satisfy this objective, and while you are at war, this objective will be unchecked. So you might go to war and be at peace several times, but to complete the campaign, you must find yourself at peace.

Objective 4: You may receive new objectives along the way without having completed all objectives. These are just "new situations emerging" as the campaign progresses.

However, if you completed Objective 4 without all other objectives complete AND your campaign was nevertheless victorious, that would be a bug. Is this the case?

I suddenly received objective 4, while objective 1 and 3 were not yet complete.
Only after I completed all 4 objectives it gave me the option to declare victory or conquer the world.
So no bug there.