I ended splitting the files, it appears that the error is due to repeated logins, long URLs, and another issue that I cannot debug due to not having access.
The server error is generic, even with modified url’s:
url of the request (removed my id from it): https://ncs-ds.avast.com/api/datastore/v2/3++++++++4
HTML Error: 413 Payload Too Large
response: Failed to write datastore. Partition exceeds maximum size
This error occurs even with only one login selected.
The Avast Team should give a more verbose error in the instance of the import instead of this generic error that makes impossible to give the correct feedback to the Avast Team