I've created an issue for this (
https://github.com/TASVideos/BizHawk/issues/831), but I'm posting it here as well.
Emuhawk crashes when reloading the N64 core if the XSplit "Game Source" is enabled and the window has lost focus at least once.
If you're running XSplit and have the "Game Source" enabled, if you load an N64 game then take focus away from the Emuhawk window, then do anything that reloads the N64 core (manually reload the core, load a different N64 game, etc), the core will fail to load and you'll be greeted with a black screen. If you then quit the program, you'll be greeted with a crash. If you do anything else to reload the core, you'll be greeted with a crash.
Disabling XSplit's "Game Source" fixes this issue but prevents optimal capture of the emulation output for streamers (as game capture is generally better than window capture. Also, window capture doesn't work properly with OpenGL mode)
Video demonstrating the bug:
https://streamable.com/j7vzd
Steps to reproduce:
Open XSplit (with Game Source enabled in the settings, on by default)
Open Emuhawk
Load N64 Rom
Switch focus from emuhawk to any other window and switch back
Reload the N64 Core in some way (manual reload, change games, etc)
You should be greeted with a black screen instead of the game you attempted loading, and if you attempt to load it again, it crashes.
This has been reproduced by a friend and I've reproduced it on multiple computers.