Speaking as someone who knows a little about Eastern Europe and the former Soviet Union, I’d say that, when it comes to problems, the EU “ain’t seen nothing yet”.
Take the vexed question of former KGB agents still around and very active in the Baltic states, as well as some East European ones. What is to be done with them? Putting them on trial is tricky and the evidence is often lacking for obvious reasons. On the other hand, restricting their human rights would go counter to EU laws.
In the Latvian Seimas (Parliament) the right-wing majority has voted to publish the names of all the former Russian and Latvian agents. The left-wing and Russian opposition parties voted against, arguing that this would divide the nation. Possibly, though most observers feel that post-Communist societies could do with a spot of lustration to come to terms and then to overcome the past.
The Seimas also extended for another ten years a ban on former KGB employees running for elected national or local positions or other public appointments. However, they also had a look at the EU legislation and decided not to ban them for running for the European Parliament as the European Union might not allow such restrictions. This could be interesting