You can't load an initial preset. At launch, your plugin initializes with the settings it has been exported with. So before exporting, load the preset you want to be the initial setting.
Yep it was an audio setup thing, for some reason my sound card preferences were messed up and no audio output was set. Might be good to output a warning message when this happens.
@Christoph-Hart Sorry I just forgot to replace it with a string... but I'm sure after testing different config with unmerged and merged time API that it doesn't come from that. Just try this string instead "2020-12-01T14:02:45" (it crashes with the string in unmerged time API Hise)