Hugrún Stefánsdóttir, out of curiosity can you find your 10K words in a version of the sdlxliff file that could be deemed more progressed, in comparison to what the cloud has?
You may find this potential file version under: C:\Users\[user]\Documents\Studio 2021\AutoSave

While it is not a perfect answer, I am trying to help you get your 10K words back.

Lyds

Hi Lyds and thanks for your answer,

The good news is that the TM seems to have kept everything, which is good, however, I don't appreciate having to re-populate most of the target segments every 2 days or so. The sdlxliff file is nowhere to be found.

Lydia Simplicio 

Further to this. It seems like the sync problem in general between Studio and the Cloud is because of my language pair English-Icelandic. You can see that Icelandic is not available in the Language Weaver:

Here are my settings (probably some are duplicates):

By the way, my options look somewhat different than they do in the demo video from Trados:

I don't have the option of 'SDL Language Cloud' at all, but rather just 'Cloud based resources'.

I never see anything saying "NMT" in the status box:

Also, when trying to pre-translate, this is what I get:

'Apply automated translation' is greyed out.

Is it possible that my language pair hinders the sync between the Cloud and Studio? Is there any way to work around it?