The reason why some stands do not show is most likely because The 'Show Stands' option is unticked for a particular Gross Area/Hall Boundary. To resolve this go to DRAW > Hall/Show Boundary > Edit Hall/Show Boundaries, look down the list to see if any of the Show Boundaries have the 'Show Stands' tick box unticked, if they do then tick them, then click close. Your stands will now appear.
Another reason they may not show is if you have moved some stands to another layer so, to fix this switch the relevant layer on and your stands will now show.