When the conflict between reddit feminists and /r/mensrights started, neither /r/mensrights nor /r/feminism had many subscribers. Reddit itself wasn't all that big yet. When it was new, its format was slightly different from the way it is now. Originally, links could be posted without choosing a subreddit. They were there, but they were not the focus for the site. They were for specialized posting when the link in question might not be fitting for general posting to the front page... but if you wanted to just post to reddit.com, you could. Both /r/feminism and /r/mensrights were created during that time, when subreddits were basically a side gig.
Contrary to feminist claims about men's issues discussion, it's been functional from the beginning. When /r/mensrights was new there was discussion about things like the Innocence Project, Dr. Farrell's writing, Murray Strauss's work, Erin Pizzey's work, etc. That was true even before AVFM had the readership or visibility in the movement that it has now. It took time for the staff to build up a body of sourced writing, and during that time it was just one among many blogs with sourced writing, all of which were regularly linked and cited in posts and comments on /r/mensrights. Discussion in the subreddit made it a communication hub for different groups of MRAs, where sources of information were offered, issues discussed, theories shared and evaluated, conclusions drawn, and even some real world activism planned. And while reddit's feminist presence divided itself among a plethora of heavily moderated subreddits (which feminist sub moderators have since labeled "the fempire,) for the longest time, men's issues discussion remained open, but centered firmly in /r/mensrights, leading to the faster and larger growth of that subreddit.
Feminists became upset that information contradicting their narrative was being shared and discussed in /r/mensrights. In fact, they didn't like any of what was going on in the subreddit, and some reddit feminists took it upon themselves to put a stop to it.
They began attacking /r/mensrights in a few different ways. Concern trolling complete with shaming tactics began immediately. There were a lot of women who seemed to think visiting the sub to state their disapproval would shame these unruly guys into silence, so there were actual lecture posts.
I wish today that I'd archived them, because it's hard to go back more than a few years on reddit, and some of those posts were really comical. One chick took the Nurse Ratched approach and demanded to know what our mothers would think if they knew "what we were doing in this subreddit." What I did eventually do was spend a little time archiving into a post titled "For the record" a set of links that includes concern troll posts and comments, manipulative efforts, and posts that appear to have been brigaded (targeted by other subreddits for vote or discussion manipulation). I'm not working on that as a project any more, having sampled a pretty good sized window in time, but if you look at today's posts on /r/mensrights, I'm sure you'll probably see some of the same things I noted during the creation of that archive.
Another form of attack was to make a sockpuppet account and post something positive that would garner emphatic responses, then edit it, changing to something that made the existing comments look misogynistic. That would then be archived and the archive of the edited post presented elsewhere on reddit as evidence of rampant misogyny in the sub. The mods of /r/mensrights had to employ a bot created by another redditor to archive posts so that there would be an accurate record when those accusations were made.
There were two results of this: One, the admins did temporarily ban /r/mensrights in its early stages, and we had to argue for it to be reinstated (it obviously was,)... and two, reddit was so inundated with complaints about posts and comments being edited to make responding comments look bad (in multiple subreddits) that they took user suggestions to denote edits. Posts and comments edited after the first 60 seconds are now marked with an asterisk, so now while you do have a chance to fix formatting, nobody can use editing to gaslight their commenters.
At the same time, there was a discussion among reddit's feminists about writing to the SPLC and asking them to declare men's rights activists a hate movement (referred to as "the MRA" because they apparently didn't know the "A" stood for Activists and not something like "Association.")
The SPLC article that feminists now cite as a declaration that the MRM is a hate movement came out shortly after that spate of edit-based gas-lighting and the reddit discussion. The speech it describes as hateful and misogynistic could just about only be what was presented after editing those posts.
Now, the SPLC itself is just a mouthpiece for the American left, for whom identity politics represents a major cash cow... and though they didn't apply the requested label, I believe the article is evidence that the organization was influenced by those demands from reddit feminists.
Even when the SPLC didn't do what feminists were asking, feminists immediately began citing the article to back the claim that the organization had labeled men's rights "a" hate group. They did that so quickly that I suspect we weren't even on the SPLC's radar until feminists started complaining about us, and that feminists have been bent on that goal (using the "hate group" label to discredit our advocacy) from the first time they heard of us.