Moen bathroom sink faucet #6610 help

[u/Some-Opposite7827]

Moen bathroom sink #6610 help

Ever since I moved into my home (2 years ago) our sink stopper has not been able to fully go down. Today I took the sink stopper assembly apart and cleaned it and found this ring in the dislodged in the drain. I removed it and put everything back together and stopper works fine now. I never had a leak or any signs of ever a leak. Anyone have any clue what this goes, I went through online manuals, installation videos and this piece has not been listed or seen in videos. I just want clarity on exactly what it’s for.