i think that censorship had an element of arbitrariness; for example it is strange that they let this one through. (also i guess 1968 was bad timing because of a clampdown that followed the invasion of Czechoslovakia)
Speaking of animated films and Russia, if you're a fan of good sci-fi and/or foreign movies, I wholeheartedly recommend checking out Koo! Kin-Dza-Dza [1]
This has to be one of the best depictions of a truly alien world I've ever seen, mostly due to how the locals behave and their strange customs.
https://www.youtube.com/watch?v=4uDtxGnYPTQ
Also they had some quite surrealist animations during the seventies, like this one
https://www.youtube.com/watch?v=iAWPgwSWEco
or this one
https://www.youtube.com/watch?v=EVtJudhNXiY