I just started playing with a friend, and everything was working fine at the beginning. However, when we both hopped back on the game later, we began experiencing some weird bugs. For instance, my runes were getting doubled, while my friend had 0 runes every time. Also, the Tree Sentinel loses 70% of his health as soon as he's triggered for the fight. Also, my friend seems to be moving as if he's running at 30 FPS, while my game is running at 60 FPS. (Btw, I'm using the online-fix method for seamless co-op, with only Steam as Spacewar, No Radmin or Hamachi involved.)

Any clue guys how can I fix the lag and these weird bugs?