9 – Why the Search api glossary field is indexed with #?

I am using the search_api_glossary module.

I have two nodes of the same content type with different titles.
the title of one node is Fysische geneeskunde and the title of the 2nd node is Fysische geneeskunde en Revalidatie

When I try to search on word F in the glossary filter, I only see Fysische geneeskunde in the search results.

When I checked it on the solr side. The node which is displaying in the search results has this value.

"ss_glossaryaz_title":"F"

But for the node which is not displaying in search results using the glossary filter has this value.

"ss_glossaryaz_title":"#"

Why it is indexed with #? And how can I fix it so that its value becomes F instead of #.

Any idea?