Odd Behaviors Using (or not using) Chromie Time?

Good day! I’ve been attempting to use Chromie Time (or not using it, too) with several characters. I’m quite lost, though, as to how using (or not using it) seems to cause several odd behaviors. A 15th level character that isn’t currently using it, seems to have lost access to just about all of the portals available in Stormwind’s Mage Tower. Are things like this phasing bugs that might often occur when using it (or not using it)? Or is this expected behavior where there are specific (and very different) rules defined for each era? It doesn’t seem to be nearly as simple as I was led to believe. Any feedback, suggestions, or a swift kick to any detailed guides that might better explain this would be greatly appreciated.

What is odd about this?

A level 15 in Present Timeline is not of a high enough level to visit any expansion after Wrath, and so cannot have a valid quest to go there,