If the concept of "Pan-Leftism" isn't in some way COINTELPRO, I would be very strongly surprised.
Everywhere it's enforced becomes nothing more than a liberal echo chamber, wherein discussions that inconvenience liberal ideology or biases get shut down. Thus continually drifting the talking point of the group towards the comfort zone of left-liberals.
Who are these left-liberals who benefit so strongly from Pan-Leftism? To put it bluntly, Anarchists, Social-Democrats, Trotskyists, and all other counter-revolutionary lifestylists. These are the groups that dominate discussions in these spheres, these are the people who get the final say on important issues. When Marxists get established in these communities, they get pushed out by the left-liberals. Often on illegitimate grounds, with strawman arguments and vast misunderstandings on Marxist stances.
Supposed "comrades" are, currently, fully backing the western propaganda out of Poland about Russia """targetting""" Poland with a missile. These same supposed "comrades" refuse to acknowledge that backing Ukraine demands the defence of Nazism. They further believe defending Russia, China, the DPRK, or any other enemy of western imperialism means you're "anti-freedom", or otherwise against democracy.
When people of differing viewpoints assemble together, the ones with the most to lose from revolutionary speech are the ones who have the loudest voices. This is inherent, aside from having a revolutionary vanguard to purge counter-revolutionaries there is no way around it. When anti-capitalists gather, the ones who benefit the most from the discussion are those who are the most disenfranchised by the capitalist system. Such as minorities, the LGBTQIA+ community, and so-on. "Pan-Leftism" inherently silences these voices, simply because allowing them to speak threatens the privileged straight whites who do not truly want a fair world, but would rather have a world that treats specifically them better. It should be no surprise that when Cuba abolished the nuclear family, these communities hardly even talked about it. And those who did controlled the narrative to either delegitimize the great victory for minority rights, or to delegitimize Cuba as being a communist state. (I.E. saying Cuba is liberalizing). Nor should it be a surprise that these communities often celebrate Rojava, but rarely mentioned the Donbas until the beginning of the war in Ukraine. Further, it shouldn't be a surprise that talk of the Donbas is mostly oriented towards calling it a "Russian satellite", rather than a revolutionary struggle against the genocide of their people.
Pan-Leftism, if it can even be called that if they exclude Marxists so easily, is a scourge on the western left that must be opposed where found. There are many roadblocks in the west in the struggle towards revolution, this is one of them. As long as new leftists flock to pan-leftist communities while they're learning the ropes of revolution, they will be tainted by counter-revolutionary talking points with no means of understanding why these talking points should be avoided.
I've got to ask where you're seeing this trend of "pan-leftism" this is a term usually meant for socialist parties under communist governments like the fatherland party of vietnam that's exclusively anti-capitalist, but incorporates lots of different socialist groups, most specifically religious organizations. I've never heard pan-leftism used in the context you're describing. Sounds like normal run of the mill white western liberalism
you must not spend a lot of time on leftist discords/forums or in leftist communities outside of Marxist-Leninist ones if you've never heard it in this context.
It’s been a few years now, but I don’t distinctly remember the moderators intimidating MLs on the last ‘unity’ server that I was frequenting regularly, but eventually I left it because of everybody’s increasing silence and disinterest. I was in another ‘unity’ server previous to that, but I don’t remember anything except for one anarchist explicitly ragequitting.
On the other hand, I have seen the moderators on one server behaving negligently when anarchists and state socialists had another petty squabble, resulting in some of the latter (and me) leaving voluntarily. That was maybe five years ago.
In any case, Discord, and social networking in general, are awful; the community’s political alignment is only part of the issue.