Sample String Maker not yielding expected results

Hi, when selecting Uppercase and Punctuation, SSM only runs through a few punctuation signs but by no means all the punctuation signs present in the typeface.
When selecting Uppercase and Symbol it doesn’t yield any result, I get the following message instead. (Mekka Scripts and Glyphs are up to date)
Subsidiary question: what does ‘in kerning mode’ mean?

Is it that SSM will only generate a pair list for glyphs that belong to a kerning group?
I added kerning groups to the missing punctuation signs and they now appear in the pair list generated by SSM
But it doesn’t work for symbols! I still get No Kern Strings Created

Mhm. It didn’t find any symbols. I will have a look.