Email with ✔ are encoded as ✔ which out puts the string literal rather than a tick.
The previous plugin output a tick (symbol). 2.40 just outputs ✔ as text because the ampersand now converts & to the html ampersand token.
According to http://www.danshort.com/HTMLentities/?w=dingb,
is a "heavy checkmark." When I put that into the content field and set the content type to HTML, I get the "heavy checkmark" in my email.
I'm not seeing it at all in 2.40 that was auto updated from within Jenkins Plugin manager. :/
Are you missing the semicolon at the end of the entity?
Yes, yes I am, I guess the last version let it through, but browsers and email clients happily display without the semicolon as well, so I guess this isn't a bug. Sorry.