InDesign will freeze if we try to open files that are online-only

Hi all, 

I hope you can help me. I have scoured the internet for solutions and none have worked thus far. 

I am a Graphic Designer and I am currently tasked with creating user manuals for my companies products. As a company, we use a shared Dropbox folder which has a vast library of asset folders, a lot of which I don't require access to as they are CAD drawings.  The preferences are currently online only (I know from previous searches that online only is sometimes the issue, but I'll come back to that) and selected sync, as I only need access to a few of the folders on the Dropbox desktop app. Dropbox storage isn't an issue as only 20.53% of 2TB's have been used. 

On Wednesday, I encountered multiple issues with Dropbox and Indesign CC.  When trying to place a file from the company dropbox onto Indesign, both the File Explorer and Indesign itself would freeze. This meant I had to Control Alt Delete and End Task. I would then open the file again, and various odd things were happening. Sometimes the file would open normally with no error messages. Sometimes I would be met with a file recovery message. Sometimes the file would open, but it would be called Untitled-1.indd. Sometimes the file would open and Indesign would ask me to re-link all of the files placed within the document, and when I tried to do this, I would get an error message about not being able to locate the file, or it would crash when re-linking. Sometimes Indesign would let me place one file, maybe two before freezing again. Sometimes Indesign would freeze or take about 5 minutes when trying to package the files. This process should only take seconds. 

When opening the Indesign file, Dropbox seemed to have trouble syncing the Indesign lock file (idlk). I would either get the error message "1 file is unable to sync", or it would just get stuck on "syncing files". The odd thing is, when I closed the Indesign file (indd), the lock file (idlk) would still show as syncing, which makes no sense. Why try sync a lock file if the parent file is already closed?

Currently the attempts I have made to resolve the issues are as follows:

The standard  IT Crowd "hello IT have you tried turning it off and on again?" fix - no effect.

I have tried uninstalling and reinstalling Indesign - no effect.

I have tried clearing the cache on Indesign - no effect.

IT helpdesk accessed my PC remotely and tried uninstalling and reinstalling Dropbox - no effect.

I have tried dragging Indesign files from Dropbox to my desktop -  no effect and this was causing the company One Drive to have sync issues also.  

I tried downloading files from the Dropbox.com website rather than the desktop app - downloading files from the Drobox.com to place them on the Indesign document do not sync, and then would freeze when trying to re-link them after deleting them from the downloads folder. 

I have spoken to our IT helpdesk company twice, and the chap I spoke with seemed completely stumped. The other colleague who has Adobe CC is also having the same issue, so it can't be my PC. As you can imagine, this is immensely frustrating to not be able to do my job, and I have lost two and a half days worth of work attempting to fix something that has worked absolutely fine in the 18 months I have worked for the company. 

My last ditch attempt at fixing the issue is to set the Dropbox folder to Offline only, so Dropbox is currently syncing 35,000+ files (around 52GB), which will take a while, so I'll update this post if it works. I am not hopeful, however, given that it is essentially the same principal as dragging files off the dropbox to the desktop. As I mentioned previously, I had already attempted this but to no avail. The freezing issue still persisted. 

So the two main issues are the Indesign (idlk) lock file not syncing properly with Dropbox, and Indesign freezing when trying to either place an image or even save, export or package the file. 

I hope someone somewhere out there in the ether can assist.

Thanks

Rob