Your subject contains the following unsupported characters
This will be now possible starting from phpBB 3.2.9 - about Emojis not Smilies.
Topic Titles
and Forum Names
, maybe also Emails
(this to be merged still) maybe also
Emails
(this to be merged still) - Also sent Emails, merged. PM me. I implemented this on my board
it requires phpBB3.2.x