There's a pretty bad bug in the game when you convert an enemy lord to your faction if they attack you while you're laying siege. If you can convert them to your faction, your tent will be left up in the field from the siege. siege preparations are still happening, so it's more like the siege UI just vanishes. Resulting in the player being left unable to move, or cancel the siege or really do anything at all. The only way to fix this in game is to wait for an enemy lord to come and attack you, which isn't always guaranteed. If I can get photographic evidence later I'll post it in a reply.