I quickly lost my caravan after the update, and thought I would add my observations along with others here.
First, I noticed my caravan unit cap had been reduced to 30 with my clan rank of 3. It wasn't attacked immediately, but after getting close to the cap it started getting attacked by bandits. After 2-3 attacks it was defeated. I unfortunately overwrote the file so I can't go back to test it, but it seemed to happen in less than a week. Npc caravans with higher unit caps seem to be able to survive easier from what I've noticed.
Second, my fief, Ortysia, was on the border with 2 warring kingdoms at the time, so I had been focusing on staying close to defend it. Initially it was losing food due to it's villages being pillaged from the start but it's been struggling to stay in the positive since. As such, I've been manually supplying food and stuck babysitting it. When the caravan was attacked near Ocs Hall, I headed over and found the area was infested with bandits. I also noticed multiple bandit groups with caravan guards as prisoners, so it's probably what Drallim33 mentioned with groups dogpiling on after getting caught. Maybe the noble's ai priorities put bandit cleanup too low when there is war, or maybe there should be something like the manhunters in warband to specialize in cleanup.
The trade skill has some really cool perks for caravans and I'd love to utilize them, but I as a player can't clean up the entire map to benefit from them.
edit: Ok, I found an older save file that was during peace time and decided to load it up and test it out. It was before I had a fief, so I was patroling around the area frequently to trade and train troops. There was also a companion party in the area clearing out bandits and presumably saved 2 caravans during that time. For the test I waited in a town and didn't intervene. 11 days from loading the save for desertion to get the party down to 30. First attack on day 27, second attack, on 38, third attack on 41, which lead to capture by mountain bandits. So 30 days from it being at the unit cap, it was captured during peacetime.