Possibly a Chinese orchestrated defection operation?
Otherwise how does a plane 'disappear'. It's one thing to lose active data link with one's own plane but given that our air defense ecosystem is crafted to track all flying objects, including non-friendly ones, it shouldn't matter if the communication was lost, it should still have shown on radar or satellite. If the fighter had been in a crash, which has become a monthly ceremony for the IAF, the crash site would still be visible on satellite. Seems like a hush hush defection and no one wants to talk about it.
Operations like these were common during the Cold War era when CIA paid Soviet pilots to simply fly their planes into NATO territory and then they would examine the Soviet hardware. At one moment, Israel had captured a Mig fighter which no one had ever seen. Their intel services managed to safely exfiltrate the family members of the pilots to Israel where they lived a life under protection.
https://en.wikipedia.org/wiki/Operation_Diamond