So far, the only serious issue I've had with the mod is that it's often next to impossible to find and reach the Marshall of your faction on that huge map before the mission times out. I get a call to join the Marshall, wait a few in-game minutes to allow him to either stand still or move, and then ask another faction Lord where the Marshall is. I can then compare his last known position from the order with his new location to (hopefully) see where he's standing or heading, and then try to find him in that direction, but there's a LOT of map for him to hide in.
It's worked in a couple of cases, and failed miserably in others, usually because the Marshall decided to go somewhere else in the mean time. Each failure puts a heavy hit on your relations, and I'm not in good graces with the King purely by way of not being able to find him several times. The times I did find him, he merely patrolled around a castle for about a week, then ended the campaign.....an underwhelming experience at best. The rest of the game has been excellent.
[ Update, several months later - Played another campaign, managed to find the King (acting as Marshall) on all but one occasion by waiting at least a day, then asking another lord where he was. In a few cases, the King had gone from deep in Russian territory to HRE land, or vice versa, in that time, so the much newer information was instrumental in locating him. On at least one occasion, a message popped up that the King had begun sieging some castle, which I NEVER would have guessed by the previous hints, as it was off in a totally different direction. Following the King on one mission, he changed plans and directions at least 3 times in about 5-10 minutes, and ended up going in almost the exact opposite direction as the one he started in. Clearly, it's a problem with the original game, not the mod, but the mod is much more heavily impacted by it.
By the way, the historical advice applies in this game as well: NEVER invade Russia. It doesn't end well. I had to reload a previous save after a combined army of over 1000 Russians assaulted my hard-won castle, even AFTER beating several individual groups of 80-150 who were involved in the siege. ]