Stop at ROM Boot

We have our own base board with the socket for the ChipX module.

Many of the units. Stop at ROM boot and is stuck there.
All these units were ok when we tested it at our factory before shipping.

We tried reseating the module etc…But then the next day or after some time it works.
Then the next day it stops again.

What condition can trigger this problem.

I am assuming if it prints Romboot the board came out of reset.
The debug port is serial

That is not usual. You need to provide more details.

How is board not booting one day then it is fine the next?!

You can always removed the module and place it on devsys for testing.