It's a well known bug, long overdue to be fixed :( The MyLog looks at the "Last Date/Time" field in the aircraft record. So, if that plane has then been logged on a subsequent day (today), then it disspears from the Yesterday log report.
What the reporting should do is search throuh the Flight records for any aircraft with a flight on that day.
Here's the SQL Airnav need to use for a "Yesterday" report:
SELECT DISTINCT
Aircraft.Registration AS "Reg",
Flights.Callsign AS "Flight ID",
Flights.Route AS "Route",
Aircraft.AircraftTypeSmall AS "ICAO Type",
Aircraft.Airline AS "Airline",
Aircraft.AircraftTypeLong AS "Aircraft",
Flights.StartAltitude AS "Start Altitude",
Flights.EndAltitude AS "End Altitude",
substr(Flights.EndTime,1,16) AS "Flight Ended",
Aircraft.ModeS AS "Mode S"
FROM
Aircraft
LEFT OUTER JOIN Flights ON (Aircraft.ModeS=Flights.ModeS)
WHERE
(date('now','-1 day') = substr(Flights.EndTime,1,4)||"-"||substr(Flights.EndTime,6,2)||"-"||substr(Flights.EndTime,9,2))
ORDER BY
Aircraft.Registration,
Flights.EndTime,
Aircraft.ModeS