Try to put NOFILTER after INTO CURSOR c_vacancylist or just after the whole SELECT put FLUSH
i.e.

SELECT apt.apt, apt.mkt_rent as mkt_rent, IIF(ISNULL(last_rent),'-',MAX(last_rent)) as last_Rent,
       IIF(ISNULL(dt_vacate),'-',DTOC(MAX(dt_vacate))) as dt_vacate,;
       apt.type as type, IIF(ISNULL(dt_vacate) AND ISNULL(last_rent),'Not found in archive file',SPACE(26)) as reason ;
FROM archive;
RIGHT OUTER JOIN apt ON archive.apt=apt.apt ;
WHERE apt.apt NOT in (select apt FROM cross WHERE NOT EMPTY(last)) ;
GROUP BY APT.APT ;
INTO CURSOR c_vacancylist NOFILTER

FLUSH