I have a similar issue. I noticed my issue today. My text messages keep failing to send. I have to try sending them several times to not have an error. Not sure if they are even going out now or not. I haven't had a response from anyone since the issue started.
I have a work phone so can test periodically and it's very much hit and miss. This is a pain. As far as sending, you can tell if it's working after you hit send. You get a confirmation on what is happening with the text in the the message itself. For me, when it's not working, it continues to say SENDING instead of SENT. My last message said FAILED.
I'm having the same problem. Incoming texts are severely delayed (hours) or not received. Outgoing texts are taking several times to send successfully.
I have a Samsung Galaxy S7. I also have an iPhone for work and have tested using both devices to confirm the lag time. Data does not seem to be affected.
Edit to say I tried restarting and Airplane mode off/on.
Note 8 I'm having the same issue. Whether using Message+ or Textra, or anything else, no Text Messages are going through or receiving. I received one text message this morning. Got nothing after that.