My spy inside my territory ambushed for some reason my vassal's envoy.

So OK, battle against my vassal, that's already bad. But this vassal never goes ahead with the battle, so I'm stuck.

I saved, left and tried to reload the game, hoping this would untie the problem (like when battles were buggy but could be debugged by doing so), but keep getting this message:

The operation was canceled.

at Amplitude.Mercury.Game.Game+<DoStart>d__4.MoveNext () [0x00157] in <4970ef3fb39e4236909ba5f6b935d1fc>:0
at Amplitude.Coroutine.Run () [0x00019] in <423cab57be344179b97cc317e43f228e>:0

So I'll go back 1 turn and hope that this situation doesn't recreate itself...