Hi Manish,
Could you please check the below notes and implement the same since I had the same issue upon punching out from the catalog to SRM system.
2041631 - Simplified Shopping Cart:Dump on Check Out From Catalog
2086844 - Dump "Buffer table not up-to-date" on Check Out from Catalog
In addition to the above, please maintain the portal information in the path as shown in the below screen shot
Kindly check and let me know on how it goes.
Best Regards,
Bharathi