If you are using save state, try saving it using in-game save instead of save state and load it on the latest ppsspp (using the in-game load feature), after it's successfully loaded and nothing strange occured you can try saving the savestate again), just in case the savestate gets broken/corrupted on buggy older version
PPSSPP Multiplayer Guide: https://github.com/hrydgard/ppsspp/wiki/How-to-play-multiplayer-games-with-PPSSPP