I'm trying to find the proximate events that might have led to the EPP changing their mind about Fidesz.
What I could piece together in this saga is
In 2019 the EPP suspends Fidesz, seemingly over the rule of law issues in Hungary.
In Dec 2020, the head of Fidesz's MEP group is sanctioned by EPP, but not expelled over some "Gestapo" comments addressed at German MEPs.
In March 2021, the EPP votes to change their rules which would have allowed them to expel the whole of Fidesz. Orban announces that his party quits the EPP and a formal letter is sent a couple of weeks later.
It seems to me that in December the EPP was still somewhat conciliatory towards Fidesz. What happened in between December and March that might have hardened their stance?