This happend to my opponent and 2x to me. We were playing a game and after a some moments my opponent told me that he was suddenly in a different game with another player, but then he was back again.
The same happened to me. I did a refresh and was back in my original game. Then there was a new player in the chat who wished hf gl. Then I got the starting screen (black with castle) and the final score screen from another game that showed I had resigned the game. It appears as if I was at the same time in another with the other player who had wished me gl and who had made me resigne from that game. Of course I was playing in my original game and didn't play in that second game.
Another refresh brought me back to my original game.
This is quite confusing and should be addressed. It's also frustrating for the other player who believes I'm in that game with him and didn't move.