Hi there and thanks for stopping by.
Since this stems form the default app, are you able to clear the cache and force stop that application? Might wanna restart it after that and give the messaging another shot. Let us know the results. Thanks!
Update: I was concurrently working with Huawei directly on the issue, and found that apparently there was an update. However, the phone did not see this update through the Updater app. Further, after thinking about it, my wife said that the phone had updated a day or so before the issue began. Huawei provided a link to the update,and after some effort (and finding out that her phone did not have the Local Update option available), I was able to install the update. Immediately after the update was installed, the issue remained. However, about 12-15 hours later, her phone went off repeatedly and delivered text messages from the last 24-48 hours en masse. Since then, the problem seems to have been resolved and text messages seem to come and go without issue now.
Prior to this, I did clear the cache and force stop the app. I also did a backup and factory reset, tried different values for the APN, switched to other apps and set them as the default SMS app and a whole host of other things. Looks like it was just a bug in the phone code (build number ending in B331), so if anyone experiences the same issue, upgrade to build number ending in D003 or later, and it should resolve after a little time.
You did quite a bit of of work on your own, but I'm really glad you got a fix for this. Thanks so much for dropping back in and keeping us updated. This is really helpful for anyone who may come across this.