I’m not sure if it’s a coincidence, but I raised a case with the ICO in the UK, and today they got back to me asking for all my communication with Reddit. Also today - after a month of silence - Reddit also emailed me with this
If you’re in the UK and had been affected by posts being restored, I’d recommend contacting the ICO. It takes less than 5 minutes
Mine are staying delete now after initially a few popping back up. What’s more concerning is that I requested my data a few weeks after I deleted my content. I was fully expecting to get empty files but nope ALL of my content. Dating back 10 years is still there! It’s not on my Reddit profile but they clearly kept it somewhere and can recall it whenever they want to. They do not delete the data.
Something like this happened for me too, but I believe these were comments that I didn't yet delete, they just weren't visible anymore. The older ones started to pop up once there was new space for them after deleting the newer ones. (On your profile not all comments you ever made are visible, only the newest/top/most-controversial ones, depending on what you sort for).
For example in my profile my very first post was visible, but none of the comments I made there. Before deleting the posts I went through each one and deleted my comments that way. There probably still are many comments from me laying around undeleted...
Mine were fairly recent and needed to be deleted several times to stay deleted. Seemed really random.