I found out why it wasn't working and it was a really stupid mistake of myself. Nothing to do with liquibase.
I insert test data through the Intellij Oracle Console. Apparently this Console by default runs everything in a transaction but doesn't commit it automatically. So what happened is that I inserted test data through Intellij, then run the script in liquibase (which didn't find any data because the transaction in Intellij wasn't committed) and then tried to see the result in Intellij. After manually comitting the test data transaction in Intellij everything worked fine.