Write to Record Smart service failing

I have a simple PM to write single record using a Write to record smart service.

It has been working fine in our lower env's Dev and SIT.

First ran into the below error after promoting this Pm to UAT. 

Error: Unable to write to or delete from the source due to system error.
Error Details: Invalid argument(s) in call

I am pretty sure the cause for this is not configure the sequence in the Record Type(couldn't test/push changes to UAT yet) .

Do you guys agree this will solve the problem? if not please share your thoughts. 

if this is indeed the root cause of the issue, it raises a different question. How did this NOT cause a issue in our dev or SIT env's ??

Pm is working fine writing new records into DB with out sequence being configured in the record type in both the env's.

Kindly shed some wisdom on this. 

Note:

1.Exact same table and sequence structure used across ENV's.

2. Only non nullable column in the table is primary key.

Thank you very much.