update: Fixed!
I took a closer look in to what was happening with the page redrawing. I've made a few CSS updates to the Attachment Manager to hopefully prevent this from happening again. The fix will be included with the upcoming UBB.threads 7.7.0 release.
note: my research returned some results regarding OSx Lion monkeying-around with the CSS overflow-y property. OSx Lion was released mid 2011. I dont run Lion, or know anyone running OSx Lion that I can run tests on. Although I have tested with iOS 9 and iOS 12. Everything looks good.
