Unable to execute multiple SLCs at a time

Hi everyone,
I am trying to process 63 SLCs from 2019 to 2024 for a region to carry out PSInSAR analysis.
When I try to create a stack with the 63 images, it throws an error , “GC Overhead limit exceeded”
I tried to resolve that by creating 3 stacks of the data with 21 in each stack using the same master for all the three stacks and have debursting them. However, I am not able to merge them using TOPSAR Merge so that I can proceed with creating the subset and interferogram formation as it throws an error : " value already present : 2"
Let me know how to proceed on the same.

It sounds as Java limitation.
Try to increase the memory used by Java in SNAP or better use computer with more RAM e.g 128 GB or more.