My daughter has an android phone, and we tested on another android so its fully android. We also tried using a few different SMS apps, including the Google Vanilla one (which she is currently using). This only seems to apply to SMS messages... Even if she sends herself a message, The first one might come through right away, but any subseequent messages get log-jammed somewhere and take sometimes hours to arrive and are totally out of order. Some dont even arrive.
I definitely feel like something account related is up. Perhaps it will take creating a new account and moving her number over?
I have 4 accounts (numbers) attached to my account and the 3 others are totally fine.
I think I may have to contact customer server.. Thanks for your attempt to help! 
Hello ChrisV,
Welcome to the community!
From what you note, it may be better to contact customer service for assistance. They might be able to reset her network settings to see if that helps.
@ChrisV wrote:
...Perhaps it will take creating a new account and moving her number over?...
Unfortunately, I don't think that would be possible. In order to transfer her number to a new account, they would need to port her number, which I don't think is possible within the same provider. If she wanted her own account, you would need to request a transfer of responsibility. On the other hand, if she wanted a different plan, she would have to change it through your account. I understand you (or she) may not wish either of those scenarios at this stage. However, I don't think there isn't a way to move her number to a newly created account.
I understand you have tested her SIM card in different devices. However, you might consider verifying her phone has the proper SMS message centre number (see here).
It's also possible that her SIM card may have become damaged. If a network reset doesn't seem to help her issue, you might consider purchasing a new SIM card. You should be able to update the SIM card details on her line through your My Account.
Hope this helps 😀
Cheers
Hello @ChrisV,
Is she using an Android phone now and was she using an iPhone before? I know when making the switch you will need to sign out of iMessage before switching. Similarly, when switching Android phones it is also recommended to disable the RCS feature as it can cause problems receiving messages on the new device.
If none of the above is related to you and since you tried another phone and you still have to problem you can contact customer service and they can look into your account to see if there is an issue.
