Lightroom doubles folders that are on my external harddrive - Lightroom wants to reimport when synchronizing

I could be wrong, but my first guess is that this is a variation of the duplicate-folder/capitalization problem I've been suffering for 2 years: https://feedback.photoshop.com/photoshop_family/topics/lightroom-2015-9-creates-strange-duplicate-ve...

It is a variation of the capitalization bug: https://forums.adobe.com/message/9354068#9354068

Every time I get it I have to go through the fix outlined here in comment #4: https://forums.adobe.com/thread/1167904

I have to jump through this hoop this every time I create HDRs or panoramas or, sometimes, sync photos from Lightroom on my phone. Often I have to quite and restart Lightroom before the reintegration of the folders will succeed without throwing an error, too.

Here's a screenshot of what just happened to me when I synced up some mobile shots from my phones. Not quite what you have but maybe of the same root cause. Note that there are two 2018-10-19 folders. On my actual hard drive, all the photos are actually in the same folder of that name.

It seems that the already known CAPITALIZATION problem was the case even though there were no obvious differences between both shown folders (hovering). But Jim Wilde ́s workaround helped anyways. Thanks Stephan and Jim and I hope Adobe will finally solve this problem in general.

@admins: I couldn't find a way to remove my two screenshots above. Can you please remove them since there are quite a few personal infos that I don't like to be visible on the internet. Thanks! 

This definitely sounds like the capitalisation problem. We all agree how you can fix this pretty easily, but I disagree that this is always a one time fix. It’s like taking an aspirine against a headache. If solves the acute problem, but it may not cure the underlying cause, because we often don’t really know the underlying cause. We know what happens, but we don’t always know why.