Board Thread:Questions and Answers/@comment-99.231.200.33-20161024212057/@comment-27247829-20161024232945

Might actually be a specs issue; I used to play on an Android phone with only 1 GB RAM, and I have the same issue like you. FGO's a bit...unoptimized in certain areas.

As for the iOS version, perhaps you should ask more confirmation from other users; we have reports on both sides, either the game's working smoothly or not at all. Considering your problem though, it's probably the specs.