It is not possible to process multiple JSON schema files using a single Data Processor the reason being the Data Processor (design) is different for each JSON schema.
You will need to create multiple DP's for processing the different JSON schema files.
As stated earlier, there will be a different DP required for different JSON schema's.
The DP code internally is generated differently for different JSON schema's which could be a reason for NULL data (if the JSON input is different than the JSON schema).
DP1 is created with JSON schema JSONS1
The input file JSONI1 is valid for JSONS1 and JSONI2 is valid for JSONS2 (a different schema).
Now when DP1 is executed with JSONI2, it might not produce the same result as the DP1 is created only for JSONS1.
To process the JSONI2 file successfully, you will need to create a new DP2 with the JSON schema JSONS2 and process it.
Hope it helps.