And in occupied Crimea and Donbass, Russian Orthodox persecution of Catholic, Protestant, and rival Orthodox groups is well documented.
The perennial issue with the Eastern Orthodox: Nationalism.
The UGCC has some legitimate grievances here. In particular the so called Synod of Lviv which which claimed to dissolve the UGCC in favor of union with the Russian Orthodox Church was as bogus as a $3 bill. During the Stalinist era the ROC suffered under the most brutal persecution in the history of Christendom and was nearly exterminated. All but a handful of clergy and bishops who collaborated to survive were either imprisoned in the gulags or killed outright along with millions of the faithful laity. So I am not blaming the ROC for what happened then. But I do blame them for not acknowledging the historical reality of that period and repudiating the false union imposed on the Greek Rite Catholics. That is both historically and morally indefensible.