I came across today one of my own comments on Reddit with a search on duckduckgo. It was still intact. The problem is I used shreddit to randomise and delete the entire contents of my account. My account comments and posts all show empty on my account pages on reddit so there should be nothing.
I did a site:reddit.com search using my username and found ~50 comments that Reddit has undeleted but also hide from my own account. I could still edit and delete them. Its curious that they don’t appear on my accounts content on Reddit and yet a search engine can find them and they are still served by Reddit. Ex Reddit users who deleted their account contents should be aware this is happening and report it as a GDPR breach to their respective agencies if they are in the EU if they too find this has occurred.
Do the comments still show after you empty your own browser’s cache too? That seems less likely to be the culprit, but worth a check to be certain.
Elsewhere in this post there’s also a helpful user who notes that the mass-editing programs can only handle a thousand comments. Is it possible this is why some of your comments are still there?
Yes, I happen to be incidentally be finding this on a brand new install of Windows as my motherboard failed last week so its super duper clean.