Since I updated to 1.50 Beta in some games there seem to be some phase lanes missing (Random Small Competitive vs AI). After my scouts had discovered all possible planets there was no enemy planet discovered, but I could track the AIs progress by the Rankings screen, meaning that they were present on this map and doing well. However, their fleet rating was always lower than mine, as if the AI already knew from the beginning that there was no phase lane from their planets leading to mine and building an accordingly smaller fleet.

This happened on several (but not all) games on this randomly generated map. It was working well until the update to 1.50. Counting the discovered planets led to the conclusion that there are around 6-8 planets which are not connected to any of those plantes I had access to, meaning there was no way of ending the game.