I am having this same issue!
I'm doing a run where I abandoned my original base and am only using campsites for my colony. Accordingly I'd set the map length timer to 12 days so I have a limited ability to grow crops.

Each time I get a raid or ambush at a campsite, the popup message "The caravan will automatically be re-formed in 12 days." However, the timer never actually appears.

Here's a screenshot of the message Errant_Gunner mentioned:

https://steamhost.cn/steamcommunity_com/sharedfiles/filedetails/?id=2282030773

huh... so i gotten something similar. I have these quests (not sure if vanilla or modded) where after you hack the object you gotta go before reinforcements arrive and i get an alert 'enemy will arrive in 24 hrs' and it never happens. Maybe its related