I can't send long text messages

[Baby got Dak]

I've used the Signal message app for a few years. and since I switched from the S5 to the S8 I cant send text messages over 2 sentences long.
I can send pictures, I can do group texting and I can receive long texts. its just sending longer texts I have a problem with. The stock message app works fine (except group texting is cumbersome).
I tried another app Textra and had the same problem. So it's like my phone has a problem with 3rd party messaging apps. Anyone else ever experience this?

 

[kate]

Long texts are MMS, just like sending pictures, so it's odd one works and not the other.

Just a guess... for Textra, go to MMS settings and switch the MMS Behavior - legacy or system.

 

[Baby got Dak]

I'm puzzled as well. I've made contact with Signal support and I think I stumped them because they just quit responding.
I've tried deleting the app, clearing my cashe and reinstalling and no luck.
I also tried your idea with Textra. No luck there either.
I hate to do it but I might have to factory reset my phone unless someone with a better idea comes along.