Q: Is AC21 filing mandatory ?

Hello I got a interesting but complex situation . I'm re-hired by my employer (A) who originally filed my green card after 5 years of working to another employer (B). I did filed AC21 when I changed the employer (With B). Now as I'm back to same employer (A) who originally filed my GC. My question is, do I need to file AC21 again or should I wait for RFE and handle that time ? Also, it gets more complex if I tell you that my original emplyer ( A, Who filed GC ) pulled the I-140 when I left the company. So even I'm back in same company who pulled I-140 , you think its going to cause any issue for I-485 ? Thanks

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