As mentioned in the comments the antennas have been changed.
Instead of a sending frequency and a receiving frequency, antennas now only have one frequency and are in receive mode by default and can be switched on to send mode.
This obviously didn't work anymore with the old AIS microcontroller.

Update:
The AIS microcontroller is now fixed to frequency 161 and will be in receive mode by default.
From ttime to time, i will switch and will send the data you set for the microcontroller in one tick, then it will return to receive mode.
So if two or more ships do send at the same time, the one that is the nearest will win, the other signals will be ignored.
Due to a random add of a few ticks to the waiting time, this shouldn't happen that often hopefully.

Okay, this took some time, sorry for that!

So the problem was that the switching between counters didn't work. It was always 1 tick sending 1 tick receiving.
That of course meant only one ship could send and therefore you only could see one other ship.
Another bug was, that the random add to the receiving time didn't work, so it also couldn't sort out itself.

Now it seems to work fine. I tested with 4 ships in total and the map on one ship showed the three other ships.

Uploaded AIS to the Workshop.