Thank you to all for the replies! I figured it out.
But first, to close the loop on the latest comments.
I asked about the .lin because I have recently added custom linetypes, although I didn't edit any of the standard linetypes. I thought maybe somehow hidden/phantom may have been changed during this process. This was not the issue.
I found that all object types behaved this way, except splines curiously. Behavior persisted regardless of PLINEGEN value.
Closed polylines did not provide dashed segments each side of verticies, regardless of PLINEGEN value. This behavior mimics how lines are displaying.
Closed shapes without verticies (ellipses, circles) work fine since they have no end points.
>>Did any of the suggestions in the link at Message 2 make a difference? Specifically, is it affected by toggling the Hardware Acceleration setting [GRAPHICSCONFIG command]?
This right here is what solved it. My sincere apologies to all for not trying this sooner. I did walk through that link when it was posted, but somehow missed the GRAPHICSCONFIG setting. When I turn it OFF, the problem goes away. Therefore, as others have identified, it was a display issue. As noted in the original post, I recently re-installed Autocad and this setting seems to be ON by default.
Thank you again to all. I still think this thread will be useful in the future if others come upon this issue.