I’ve experienced a similar issue, and here’s how I resolved it:
When starting up the systems, avoid turning on DL (Datalink) and MIDS LVT right away. Wait until the alignment is completed and the INS is set to NAV. After that, turn on DL first, followed by MIDS LVT. Within a short time, friendly aircrafts should start appearing on the system, and your wingman will also appear shortly after takeoff.