Hello
I switched my employers before I-485 approval. I changed the employers after 1 year of filing I-485 using AC-21 rule. I was questioned about this in my citizenship interview and it was not an issue for approving my citizenship application. The officer asked me if I notified USCIS about my employer change as she did not find any documentation indicating that. I said to her that I called USCIS to inform my address change and employment change, which i did. The officer asked me if i changed the jobs in similar category and then recommended to approve my citizenship. You don't need to worry about your employer switch, the whole purpose of granting green card to give you freedom to work for whom ever you like provided the job classification is same. My advice to you is be confident when answering the officer if officer asks you about employer switch. If the officer sees you hesitant in answering, it might trigger additional grilling.
Don't worry and be confident, you will get your citizenship. Another thing that will help you is get an employment letter from your current employer to match your labour certification.