"MAP" stands for "minor attracted person", basically rebranded pedophilia. People using this label have existed for a while in relative obscurity on sites like twitter and tumblr.

Then 4chan and other sites with lots of alt-right users decided to spread the narrative that MAPs are actually a massive group that's succeeding in joining the LGBT community, in an effort to associate gay people with pedophiles. Some users on reddit and elsewhere have bought into this narrative uncritically and have decided that they need to spread the word about MAPs sneaking into the LGBT community everywhere they can.

Problem is, there aren't many actual MAPs, and they have been rejected instantaneously by the LGBT community wherever they have appeared.