I can confirm that the second game appears to have synchronization issues in general. In my case, I first observed the second game was running 5-10% fast when trying to figure out why it sounded odd. After trying to proceed further, at some point the frame limiter came off entirely, and the game ran at ~5000fps, while the original window continued to run correctly at ~60fps.

Version 0.10.0 Windows 10 64-bit, as well as latest development build.

That's unrelated. There are known synchronization issues, but this is about being "able" to link systems that aren't actually compatible.

If the multiplayer opened is a GBC game it gets speed up. I tried to use it with two GBC games and this same issue happened.

Again. Not a related bug. You should file a separate bug report.