I have literally never seen it.
I'm not saying it doesn't happen, but it doesn't happen in the places I frequent - and I frequent a LOT of Leftist communities.
Edit: People are pointing to the Tankies Lemmy community. The place designed for tankies. I'm not arguing they don't exist. I'm aruing against the people saying they're all over the place and pervasive in other communities and that they're not a commonality and not the usual communist/socialist.
Pointing to the Tankies communities doesn't change anything I've said.