Elon Musk, who owns X, formerly known as Twitter, had some of the highest rates of posts criticising Jews, according to research from the Online Hate Prevention Institute.
"X was generally difficult to work with, particularly from Australia," chief executive Andre Oboler told the royal commission into anti-Semitism on Wednesday.
He said Mr Musk's purchase of X in 2022 resulted in almost 80 per cent of trust and safety staff being fired immediately.
Since then, anti-Semitism on the platform had grown.
Mr Musk has previously denied accusations he is personally anti-Semitic or racist, claims levelled in 2023 after he posted in support of a conspiracy theory involving Jews.
Dr Oboler's team, which worked with a far-reaching definition of anti-Semitism that included anti-Zionism, identified there was a correlation between pro-Palestine activism and harmful rhetoric, although one didn't inherently lead to the other.
"I'm not saying that all those activities are anti-Semitic - far from it," Dr Oboler said.
"But there is a segment of anti-Semitism that goes on the bandwagon with that (activism) - and when there's less activism, there's therefore obviously less opportunity for that anti-Semitism to rise."
The third block of public hearings for the royal commission began on Monday with a focus on the treatment of Jewish people in mainstream and social media.
The ABC and SBS will appear later in the hearings, along with dozens of Jewish Australians who have been subject to online hate.
Experts in social media, online hate and extremism are appearing throughout Wednesday.
Others detailed to the inquiry on Tuesday how the vitriol spreads.
Social media users who engaged in anti-Jewish conspiracy theories were more likely to post material containing hate speech, expert Matteo Vergani said.
The Deakin University associate professor called for the targeting of hate "clusters", saying it would be a more effective way to remove anti-Semitic content from online spaces.
"Trying to address individual posts containing hate is like emptying the sea with a spoon, because there are too many,'' he said.
"So the only way to have a cost-effective intervention is to identify the clusters.
"It's a great opportunity for us to start monitoring online hate with a stable infrastructure, because if we understand how hate spreads, we can really intervene in the most effective and cost-effective way without having to use censorship or other hard and draconian interventions."
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