I opened a HI ticket about this and they communicated that the global text search does not respect more non-alphanumeric characters.
It turns out that the keyword search doesn't respect _ characters.
Meaning if you search for "this_custom_word" and you expect to find results, if one of those words is on the Stop list tables (ts_index_stop, and ts_stop). It may not show up.
Something HI made me aware of. I askd if they have other delimiters, but they said _ and space are delimiters.
If I get more information I'll update this.