38 out of 90 Vietnamese tourists with ”no visa” have ”disappeared” in Jeju, South Korea

It has been revealed that 40% of group tourists from Vietnam who visited Jeju, South Korea, using the visa-free system did not board their return flights.
According to the Jeju Tourism Organization on the 3rd, the man entered Jeju from Nha Trang, Vietnam on a Vietjet Air flight on the 14th of last month.
Of the 90 or so Vietnamese who had been sent home, 38 did not board the flight home. The Vietnamese suddenly lost contact and disappeared at the last tourist spot they visited before boarding the flight home on the 17th of last month.
They are allowed to enter Jeju without a visa and stay there for 30 days, which expires on the 14th of this month. If this period passes, they will become "illegal residents."
The Jeju Immigration Office is currently trying to track down their whereabouts by checking CCTV footage.