Logged out of the Dropbox app and back in and now I have a 'Dropbox (old)' and a 'Dropbox' folder

At some point in the past few weeks, I was automatically logged out of my Dropbox account. When prompted to log back in, the app setup process began as if the Dropbox app was not already installed on my system. I tried force quitting the app and restarting my computer, but this didn't solve the issue.

I tried following the prompts. I was presented with a message stating that I already had a Dropbox folder set up on my machine. The menu didn't provide me with the option to use the existing Dropbox folder. Instead, it only offered that I rename my original folder something else, or choose a different location (same menu the OP screenshotted above).

Ultimately I uninstalled Dropbox causing my existing indexed folder to become hidden. When I reinstalled Dropbox, it created a new Dropbox Folder on my main boot (C:) drive (my original folder stayed hidden on my larger (D:) drive). When Dropbox was installed, I tried re-assigning the new Dropbox folder to my (D:) drive, but the app would immediately crash, I assume because it saw the other Dropbox folder there.

Ultimately I resorted to renaming the original folder "Dropbox (old)" and allowing the Dropbox app to create a new Dropbox folder on the same drive. My Dropbox (old) folder contains 1.25 TB of data, 522GB of which is on my local disk. There are 71,000 files and 5,900 folders. I'm wary of the process of re-indexing this data to the new Dropbox folder. 

It should be noted that, unlike OP, I'm not being repeatedly logged out. My primary concern is the possibility that some of my files on my Dropbox (old) folder haven't been uploaded and synced, and will be lost if I allow the new Dropbox folder to overwrite it. Why can't I simply reconnect my existing Dropbox folder to my online account? Why does the app not allow for this? This is the first time something like this has happened. Dropbox has worked really well for me up until this point. But this breakdown in functionality feels bordering on catastrophic, especially if I were in the middle of a project (thankfully I am not). If there's not a clear way to proceed, I will probably just move my data to my GDrive account and call it quits with DB.