Clicking on the '+' icon in the workflow editor opens a form which has a "Submit" UI action. 

 

The Submit UI Action which appears in the pop-up form is on the "wf_workflow_version" table. 

 

This UI action has a script in which it calls another UI action on line:10 (var SYSVERB_UPDATE_GLOBAL = "42da42d00a0a0b340066377beb6dd099";) which is on "Global(global)" table. 

 

Check to see If the second global Submit UI Action is inactive in the instance. If it is, make it ACTIVE in a SUBPROD environment first.

 

Also, if the Submit UI Action is customized then revert it back to OOB in SUBPROD. 

 

After doing the above please clear the cache. This can be done by typing in cache.do in the left nav.  

 

Once that is done check to see If the customer is able to submit a new workflow without any issues.