What's causing req lines to get stuck in Auto create?

Hello:

We use automatic PO creation utilizing the Create PO workflow process. Reqs are normally created, imported, then a standard PO is automatically created by the Create PO workflow process off a global BPA.    We're finding a number of req lines sourced as supplier are getting stuck in auto create even though they have a valid sourcing rule, global BPA, and a source document # attached to the req line.  This requires buyer intervention to auto create the PO.

 
The only commonality I can find in the req lines that are getting stuck is that all are on internal reqs with a mixture of lines sourced