This is weird to say the least. Let's try and game plan why to turn on their AIS for any other reason than a deal with the US.
1. They didn't do it willingly, ie, someone hacked the Iranian system and turned them all on. I don't think this is the case because they don't spoof locations as much as just turn them off.
2. This is a response to the latest set of UN sanctions reapplied to Iran. No AIS provides stronger legal basis for other countries to inspect or seize an uninsured Iranian vessel.
3. This could be a China ask as a good faith offer to the US... Not sure how this helps either side with the timing
4. Could be Iran daring others to stop them from dealing with China and forcing China to step in
None of these make a lot of sense, but then again, Iran all of a sudden making a deal with the US to remove sanctions on oil exports would require a ton of moving parts that would have already leaked.
Going to put it in the weird but need more information pile for now and see what is going on in the morning.