GraphQL playground - how to filter by the presence of certain symbols in a field?

When filtering my results by strings of text, everything works as expected.

But when I look for symbols like the bullets or certain tags within my ‘html’ field, it just doesn’t work

where:{html_contains:"foo"}            <--- returns expected number of records 
where:{html_contains:"•"}              <--- returns every document, bullets or not
where:{html_contains:"&bull;"}         <--- returns no documents
where:{html_contains:"<ul>"}           <--- returns no documents
where:{jsonfield_contains:"foo-bar"}   <--- returns no documents

I’ve been told my problem could be that the field might be RichHTML, so do these problematic symbols have a certain code that could be used instead to find them?

Yet even when the field is json (plain text, right?), I still can’t search for symbols such as a dash.