Off hand - Sounds like the MMS is still occupying the network cache & until it has cleared - You are unable to send an SMS....
You could test my "world renowned Cache Clearing theory" (inside joke - sorry) by doing this:
Send an MMS - Then wait a second - Toggle Airplane Mode On & Off - Send an SMS - If it works - it would suggest that my "hairbrained" Cache Clearing is valid - Let me know if this "resolves" the issue/question 🐧
You're onto something, but maybe not conclusive yet Smiling_Face
So it definitely works after switching airplane mode on and off. But then after that, it's almost 50/50. It can keep working (sending mms then sms) , or it will fail on the next attempt. I might add, that sending mms after mms always works.
I'm thinking that for some reason - Network cache is not getting cleared automatically after sending an MMS - The suggestion of Toggling On / Off Airplane Mode wasn't intended to be a permanent solution - It is to try & verify that it was likely a Network Cache issue.
Does this ONLY occur when you are at your Condo?
You could also Contact Koodo & ask them to Reset your Network on their end...
Are you using Samsung Messages? If so - You could download Android Messages from the Play & test with it - Send an MMS & see if it allows you to send an SMS immediately after - Without Toggle Airplane Mode On/Off.
Don't remember if you tried this - But you could also try Booting into Safe Mode & see if you can send an SMS after sending an MMS without Toggling Airplane Mode - Would rule out any 3rd party apps causing the problem..
But I think that maybe we are on the right track to figuring this out 🤞🐧
Let me know how the above suggestions work out 🕊️
Just another thought - Check your Network Settings as seen in the attached Screen Shots - You may need to verify that your device is using the correct APN for Koodo & Check to see what your Preferred Network settings are & if it's "autoconnect" 🤙
Thank you for all these suggestions, I will definitely try them. Yes, it only happens in my condo, not even in other buildings or houses Smiling_Face It all started months ago when 3 things happened. I switched from note 4 to s9+, then from public mobile to Koodo, and finally bell installed 2 very small boosters outside the building as part of installing fibre internet in the building. I'm still thinking it's a koodo/signal issue, but I'll keep investigating.
Are you aware of any sms app that will show a detailed log of why an sms fails? I've tried samsung, android, textra and pulse, and can't find an error log.