Rock based and Ace2 based Cart's can't talk to each other. By design, working as intended. Somewhat related to next point, somehat to fix constant stream of data that no one may use. (If no one has their map open, who cares where you are?)
When you open the map, Cart sends a broadcast to your guild, asking for positions. Guildies running Cart start broadcasting their positions as long as someone running Cart has a map open.
Basically, your guild needs to pick a Cart version (stick with Ace2 or upgrade to Rock) and it'll start working normally again.