In commit https://github.com/julianstorer/JUCE/commit/e253b8bea170cd017c277ba244c0b7b217d4d39e an assertion was added to Component::grabKeyboardFocus().
This assertion is triggered by the windows FileChooser when the native dialog with a juce component as the FilePreviewComponent is used. In juce_win32_FileChooser.cpp this code triggers the problem (starting on line 214):
if (extraInfoComponent != nullptr)
{
flags |= OFN_ENABLEHOOK;
info.customComponent = new CustomComponentHolder (extraInfoComponent);
info.customComponent->enterModalState();
}
This probably means the keyboard focus is not working for the previewComponent and the windows implementation most likely needs a fix.
