I also have tried sprouting them. I planted 10 lychee seeds in pots (peat + perlite mix), along with 10 longan seeds. few lychees germinated but they died soon after pushing out. Most longans germinated but died very soon after pushing as well. No sign of bug damage. Only one longan survived with 4 leaves now but it is sickly looking. Maybe they cant take the 115F heat (they are under 50% shade cloth).
Longans that I germinated indoors that all germinated and are looking good (controlled lighting and controlled temperature.
Interestingly, Sapodilla seedlings are taking the heat like champs. I thought it would be the other way around but what do I know
Will see it they can take the 120-122F in July.
Location: Zone 10B in extremely dry middle eastern desert.