Hello,
I'm also using a OP5 since a few months and I also have MMS issues. In my case, MMS have an unknown status, and aren't sent. The worst is that it comes and goes and you never know if the device will receive MMS or not.
My trick to fix it is to switch mobile data off, then go in the AP configuration and reset them. The mobile is then tuning them automatically. After that, I switch the mobile data back to on state and the trick is done.... at least for a time. 😕
Hope this could help...