Excel File Validation in Appian- readexcelsheet function

Hi all, I am using readexcelsheet function to read the excel sheet and perform validation at row level to identify the duplicates, checks to identify whether the mandatory fields are present or not  . And then populate the value on read only grid with the errors for each row  before uploading to Database .  When we are uploading file size of ~100 KB , the code is getting executed successfully and the grid is getting populated after the validation and we are able to load the valid data in the DB  . However, the user wants to do a bulk upload of 96K records (~ 6MB file) ,in that scenario, it fails on the site level  and gives "403 error- You don't have permission to view this page".  We tried uploading 10K records ( file size ~300 KB ) and got the same issue . We tried to execute the readexcelsheet function without any validations and then also it gave the same error on reading 300 KB file  . Is there any file size limit for the readexcel ? Could you please suggest any alternative approach on how to read the excel , do the validation before uploading to DB for faster execution  . We are using the version Appian 20.4  

Any help is appreciated. Thank you .