There are multiple reasons that the data you are looking for is not showing in a filter dropdown.
1.) There may be too little traffic to the specific page/campaign/etc. Each site setup is limited by a "site size". This is done to limit filter dropdowns from showing EVERY single page name that may come in, in case of a misconfiguration, or in case of extremely granular page names.
2.) The data may be too fresh. If you are looking for the page name the instant after implementation, it may take a while for any tag updates to propagate to the wild. Just give it some more time!
3.) Filters can only display up to 200 rows. If your data is too granular, there is a possibility that there are too many entries than can be displayed.
4.) Check your date range! The option you are looking for may not have existed on the specific date you are looking at. Filter dropdowns update dynamically based on date range selected.
5.) Check your combination of filters. Certain traffic segments(and other categorizations) may not include hits to newly created pages if they differ in segment.