If it isn’t on purpose, then they have a bug that is restoring comments. My main account is 18 years old. Cake Day is December 2005. I deleted it all, and then I checked from multiple devices to ensure when I logged in it was all gone, and it was. Until it wasn’t. I had about 100 random comments from 2013 to 2022 come back. So I manually deleted them all… again. And then a few days later, suddenly different comments are back. I must have repeated this deletion process 4-5 times. Each time, Reddit’s interface (not a third party script or app) showed me everything was gone… until it wasn’t.
They have some automated recovery going on whether they want to admit it or not.