Log Analytics custom logs json format

Question

Hello, 

A customer is trying to upload custom log files in json format to a Log Analytics workspace using the file based upload method (Windows). But after a few days the ingestion type changes to Ingestion API and the upload stops.

I'm not sure if this behavior is expected or if its even supported to upload json files via file based upload. Can anyone enlighten me?

Thanks in advance.

BR,

Martin