FB, Instagram, WhatsApp blocking Iranian accounts, even outside the country

From context we can tell that they used to be working before the protest broke out, so the explanation must be something else.

Yup, there's also a slew of companies rescinding offers to companies in these regions lately as well. I think there has been some tightening of sanctions recently or something.

They were working before. Chat applications are not sanctioned.

This is Facebook actually violating sanctions by helping the Iranian government.