I believe there may be limits on each GET or POST so the solution is to treat it like pagination and grab, say, 100 at a time. I’m not entirely sure of this - I just recall reading something about it in the forum a long time ago.
Also, how are you loading the data? Using the run a workflow on a list, or the new Data API Bulk Data Loader? I wouldn’t be surprised if the prior is rate limited and the latter is much easier and faster to load 10k entries.
Here’s a working example of the Data API Bulk Data Loader if that’s helpful: How to write data to BubbleDB using Data API Bulk Data Loader
Best of luck!
Scott