Why is my 8900 behaving like this?

Strange behavior. Every few weeks my Aqua Terra 8900 stops between dates at midnight. Once, I corrected it easily and it ran for a few more weeks until it happened again.

Then I brought it in, and the watchmaker did what I do and said there's no problem.

Next time it happened, I didn't manually correct it and it advanced to show the next between-the-dates pair. Then I corrected it.

Last night it again stopped between the dates at midnight. And I left it like that to show the AD.
BUT sometime around 9 pm the date wheel advanced to the proper date. And then at midnight it advanced again and everything looks fixed!

I am wary of sending it in and having it opened because the problem is so ill defined, I think.

Someone had this problem/ phenomenon? Does anyone know what's going on?

I feel that they'll do whatever they do and 4 or 6 weeks later this will all happen again because they really didn't know what or where the problem is.

Your AT clearly has behavioral issues and needs therapy. You should send it in to Omega for warranty service and take pictures or video of the issue if possible.