Fetch seems to wait for a previous fetch to finish

I have a really weird situation in react-native. When I trigger a long running fetch (POST to upload a photo) it seems that the ones I do after (GET to fetch data for exemple) are waiting for the previous one to finish.

I check the UI & JS threads and I have 60 FPS on both.

Does someone have a clue on what happens in this situation ?

Thanks in adavance.