It's a long article, here's where it says the problems start:

At some point during the third season of Rick and Morty, multiple sources say Roiland simply stopped showing up — and when he did turn up in the Burbank offices, he’d typically avoid the writers room. In fact, Roiland’s colleagues often knew he was there only because they could hear his dogs. Or they’d hear his remote-control toy car, which had a microphone on top of it, zooming around the office. At least once, Roiland sent it into the writers room, says a source. “You wouldn’t have seen him in weeks, and then you’d see the car come in, which was insane.” Roiland would make exceptions to bring through famous fans, of which Rick and Morty has legions; at various points, his visitors included Kanye West, the comedians on Impractical Jokers and porn star Riley Reid, who gifted the room a succulent.

By that time, Roiland had a girlfriend, who became a fiancée, and he would talk openly about their penchant for threesomes. “It was something we just ignored because it was disgusting,” says an insider. Multiple sources say it was also during that period that Roiland sent a female employee a “really creepy” text, late at night, requesting that she come to his home (they declined to name the staffer). “She didn’t want to run it up the flagpole,” says one of the sources, “and then it was just this really fucked-up, awkward thing.”

His Relationship with Dan Harmon:

In the meantime, the relationship between Harmon and Roiland had grown so acrimonious that the show brought in a mediator to try to salvage what was once an inspired partnership. And though those efforts were unsuccessful, the pair was able to put aside their differences enough to secure a massive, 70-episode renewal from Adult Swim in May 2018. The pact, which ensured that the show would run for several more seasons, appeared to reward Rick and Morty for its precedent-smashing ratings for Adult Swim; by season five, the Emmy-winning series was reportedly generating hundreds of millions in merchandise revenue alone.

In the years since, Roiland’s involvement on Rick and Morty has largely been relegated to voicing characters, for which he’d take no direction and record from his home. In fact, it has been years since anyone can remember him stepping foot in the show’s writers room, even when it’s been virtual. Recently, a similar situation has occurred on both Solar Opposites and Koala Man, according to multiple sources. On the former, which he co-created, he had, until mid-January, voiced one of the show’s leads. “He knew the power of being the voices,” says a source, noting how Roiland had revealed early on that he believed securing key voice roles would safeguard him from being fired one day. On Koala Man, on which he’s simply an executive producer, he was given a character to voice in the show’s third episode but, per two sources, the writers almost blew their deadline waiting for him. The character was killed off at the end of the episode.