I’m having a very similar issue. I installed the FAQ plugin, tested it and then decided to get a license in order use + – as toggle symbols.
Before adding the license I saw the + – toggle symbols in the settings (but could not select them). Now with the license installed I only see the alphabet as toggle symbols (and can select them).
How can I get the correct toggle symbols?
My site is here: https://www.la-palma-sailing.com/de/faq/
Another site on the same server actually works correctly: https://www.itigo.ch/faq/ but I can’t figure out the differences.