Workflow sporadically not triggering

Hi all,

I'm looking for some assistance with an approval workflow that I developed. It is currently set to trigger when rows are added or changed, when "Employee Name" changes to Any Value (see image).

Out of a list of 95 submissions, the approval workflow did not trigger approximately 20 times. The "Manager's Email Address Approval" field is just blank.

Has anyone encountered this before? What am I doing wrong? Thank you