Why are my genes filtered for Gene Ontology term enrichment?
What is "click here for details" saying? That link should contain an explanation of what happened.

GSEA usually requires entrez_id to run. If your list contains gene_symbols, then before enrichment, you need to convert the genes names. This can and is (always) tricky as genes are known with different names. For example, by googling I couldn't find any AASS3 gene, but I found AASS, which is also named LKRSDH,LORSDH, and LKR/SDH. Depending on the software you are using for conversion, and the genome version used some genes will be missed. I usually run (in R) a combination of geneSynonym and biomaRt to fill the gaps in the lists.  

Even better, would be to use ensembl_id or even better entrez_id directly