AIS tracking sites get their data from AIS receivers that are installed along coastlines as well as satellites. Satellites receive a very low percentage (<2%) of transmissions from standard AIS transceivers and have many blind spots. Therefore tracking sites do not provide full coverage, at times their reception range is variable, may drop out entirely and their data refresh rate cycles and latencies can be very slow.
The best way to check your AIS is working correctly is to ask a nearby vessel with AIS if they can see you.