you'd better use EAD from AOS

For this question, differennt people have different understanding and it has always been very confusing. I believe that your status is changing to AOS after you use AP to enter US. You might be able to use your EAD from OPT if no one notice that. Officially, your F1 is lost when you used AP. I had similar experience and now I use my EAD from 485 pending to finish up my Ph.D. study. Everything is fine now.

If you want to be safe, it is better for you to apply for EAD based on I485 pending before you leave US. Then you can notify your HR department of your new status. The only thing you need to do is bring your EAD to the office and let them keep a copy.

Don't worry. You don't have anything to lose but to gain freedom from your 485 pending status.