My understanding is that time outside the U.S. of more than 30 days while in J-1 status is permissible but triggers a SEVIS alert and requires the ISSO to verify in the SEVIS system that you are continuing with your J-1 work while outside. So, you would want to advise the ISSO before you leave the U.S. and get his or her okay.

Not an attorney so I don’t know the details but it is definitely possible to leave the US several months in a row on a J1. When I did it (also as postdoc), it was an involved process that escalated to the (vice?)president’s office to get permission so there are clearly questions the university needed to address... I didn’t have any visibility into it all but what I was told about regarded taxes mainly (since getting paid abroad).

So technically possible but also a tall ask (I didn’t know at the time of asking and my PI went with it).

I then came back and carried on without any immigration issues.