Output issues with Medela Freestyle Hands Free Pump

Hi, FTM here with a 3 week old.

I have been using a Medela Freestyle Hands Free Pump once a day and noticed significant output issues between breasts. It's a brand new pump so I don't think it should be membrane or cup issues. I have tried tighter bras, repositioning the cups during pumps, etc. But every time I've pumped over the past few days I've gotten only like .5 oz from the left breast and 3-4+ oz from the right breast. I'm otherwise able to breastfeed my baby from both breasts with no supply issues, so I also don't think it can be chalked up to an overall "slacker boob" issue.

Should I try pumping one breast at a time to see if that helps with potential suction issues? This doesn't seem like a long term solution but I'm willing to try anything. Should I just ditch this hands free pump and go back to my Spectra S1 to compare output for a few days? The only other thing I can think of is that I need smaller flanges/inserts for the cups. I'm measured at a 19mm but I'm using the 21mm cups. Could something like that really be the culprit for such different breast output with this pump?

Long term I'd like to continue to be able to use this (or another) hands free pump -- but I'm open to any and all recommendations.

Disclaimer: This has been cross posted in r/ExclusivelyPumping.