Note: a stack trace w/o debug info is not very helpful. If this issue persists I recommend to deploy an executable from a debug build (assuming that you build the executable and not the end user).

KiUserExceptionDispatcher is not defined by FLTK. This indicates that the handle() method of your derived window class calls KiUserExceptionDispatcher().

7: Fl_Window::handle - 0x140709297099744

I have no idea why Fl_Tiled_Image::draw() would (indirectly) call Fl_Window::handle(). There's some clipping done, hence fl_win32_xid() might be plausible.

8: Fl_Window::y_root - 0x140709297101632
9: fl_win32_xid - 0x140709297228272
10: Fl_Tiled_Image::draw - 0x140709297052528

Fl_Tiled_Image::draw() may be called (IIRC) when the 'plastic' scheme is used to draw the background image

 IMHO the best you can do is to use a memory analyzer like Address Sanitizer (ASAN) or valgrind to check for access violations in thorough tests. IIRC Visual Studio supports ASAN, hence you should be able to build your program with ASAN support on Windows, and I'd guess that MSYS2 also supports (clang and) ASAN.

I hope this helps. Good luck.

-- 
Gonzalo Garramuño
ggarra13@gmail.com