Hi there. I've update to the latest one 1.11 and using PHP 7.2 the issue still here, as before (when there's HTML signatures).
My workaround still working for some people here witch is great but on my case don't work.
I got my issue fixed with the comment here: https://forum.osticket.com/d/92969-subject-shows-content-empty/7
After I've downloaded the file "mimeDecode.php" from that website and place on the server, all the emails are received correctly on the ticketing system (visible through the Agent Panel and also through the emails the Agents receive).
I hope that helps OSTicket to fix this once for all, because from what I was able to search, it seems the issue still here since last year.