We recently have changed the version of Jira from 7 to 8.
After that, I notice that in the Epic link field, the suggestions of Epic have changed.
The suggestions look to rely on words rather than started letters like it works for fuzzy search.
In other words, Jira waits for a whole word before suggesting corresponding epic names.
Before he suggested the corresponding epic names from the first letters.
See screenshots.

Do you confirm that ?
Do you know if it can be changed ?