[!AjaxSearch? &ajaxSearch=`0` &parents=`100` &depth=`1` &landingPage=`8` &addJscript=`0` !]
1/ Are you sure that this is the snippet call used on the landing page (#8) ?
2/ Are you sure that all the documents below #100 are:
- searcheable
- published
- allowed for this user (public or user allowed)
- not deleted
If yes,

then
A/ try &parents=`in:100`. The older form should be compatible but ...
If it still doesn’t work >:(
B/ add &debug=`1`, ru a search, open the debug/ajaxSearch_log file, and check the where clause of the SQL statement executed. Something like :
WHERE ((sc.id IN (26,27,28,29,30,31,32,128,129,130,131,132,135,136,266,137,138,139,140,141)) AND (sc.published=1) AND (sc.searchable=1) AND (sc.deleted=0) AND (sc.privateweb=0))
You will see where the search occurs. You could then re-run this SQL statement in PhpMyAdmin to check the results.
In your AS snippet call, &addJscript=`0` is useless with the non-ajax mode (&ajaxSearch=`0`). You can remove this parameter.