So an iPhone-wielding friend wants to send me a picture of her dog. She takes a snapshot and sends it to me as an MMS. Yeah, old school, I know.
Now for some reason, this ends up as a group MMS on my end, in a separate thread from her text SMSes.
And if I reply with a few words, one minute later my phone buzzes, as I get my own message back in the "group chat". And another minute later, it buzzes again, since I now get my own SMS back.
If I want to reply with a picture of my cat, I'm not even allowed to.
The stupid, I don't even.
There are plenty of online advice telling me to open the messages app, click on settings, then on "more settings" which I don't have, or "MMS options" which I also don't have, or on "advanced" which I do in fact have, but below that, I'm still missing any options for group chats or MMSes.
So as far as I can tell, messaging is totally borked on Android - or at least on my Moto G5s. I'll probably have to ditch the cheap piece of crap - sadly, because it is otherwise a decent phone with a good camera, especially at the price. A shame since it's obviously just a software thing, which could have been fixed pretty easily. So, if anybody can point me to a messaging app that has absolutely no support for RCS or SMS+, I'm happy to return to the happy past where things actually worked.
@ketil
Are you certain it's the app's fault? I ask because I had some bad MMS experiences a few months ago, and it turned out that the two (UK) mobile providers were doing nasty things to MMS messages.
For MMS messages outside their network, all the receiver got was a plain SMS with a link. So I'd be paying something like 40p to send an MMS and all they're actually send would be a plain SMS text. When I complained about it they said this was now the expected behaviour on their network.
@ketil
All of which makes me think they're breaking MMS and don't have a clue what they're doing.
I don't know if it's related to the problems you're experiencing but I hoped a few more data points might help. (In the end I gave up trying to use MMS and I stick to WhatsApp the days.)
@OpinionatedGeek
Not entirely sure whom to blame, but I am able to receive MMSes, it's just that they get organized really, really stupidly. If it was idiocy on the part of the network provider (entirely plausible), the app should be able to work around it.
@ketil Yeah, I don't think SMS gets a lot of love from the Android team.
@ketil look into f-droid.org 
Not helpful: https://help.motorola.com/hc/3583/444/global/en-us/T1411100853.html
Also not helpful: https://www.komando.com/tips/376034/put-an-end-to-annoying-group-texts