Firestore collection missing after export

Question

I export my database like this:

gcloud firestore export gs://xx.appspot.com/asdcx
gsutil -m cp -r gs://xx.appspot.com/asdcx ../../../
firebase emulators:start --import ../../../asdcx

This used to work quite well. But since a few days after changing some fields I can't get one of the collections of the database to export at all. The other collections export and work successfully. The collection that doesn't work is quite large (50k documents). I see it in the web UI yet if I export it this way and try to find it in the emulator UI - it's not there and I can't access it locally. I see it on the web UI for firestore but if I try accessing it with my code that also doesn't work. Why does that happen?

Edit: FB debug file shows this

Failed to send a new message due to too many pending messagings in the back channel (10001). May need enable flow control.

I also noticed that the firebase export produces a single file of 140 mb -> output-0. Usually it was in more chunks of those output files. I don't really understand how to set that but it seems to be set automatically and it might be the reason why I can't load the data (maybe too much data in a single chunk?)