I count 15 of this type currently in the air worldwide. When airlines have an aircraft type change, flight plans aren’t updated?
It seems some 737-800NG are identified as MAX versions.
ADS-B messages do not transmit the aircraft type, so live tracking relies on database info, maybe those have errors.
One would expect you have to file the correct a/c type in a flight plan. Maybe those are relocation flights with a special permit?
The public data often relies on schedule or status data from the airlines, rather than the flightplan, which is not updated to reflect the specific 737 variant when it changes in some cases.