I recently upgraded from a Samsung Galaxy S8 to a Galaxy S10e. I am now unable to send MMS while on Wifi and they are very slow to send while Wifi is off. I used the native messages app. During debugging I switched to Verizon's Messages+ app, and experienced the same issue. Oddly, I am able to received MMS with no delay. I believe the underlying issue is that data signal is suddenly weak. This is occuring in my home where I never had a problem with the Galaxy S8. The S10e was purchased from Amazon as a refurbished phone. I moved the sim card over myself (voice and text service work fine so I am confident that the sim card is seated correctly and not damaged) Has anyone else experienced this? I am getting close to returning the phone and assuming I got a bad unit, but I'm also wondering if Verizon is throttling my data since I moved the sim card on my own and avoided their "Upgrade fee". That sounds somewhat paranoid, I know.
I'm sorry to hear that you're having issues with your messages. When was the last time you picked up a new SIM card?