bug in bulk convert

Hi,
when i bulk convert there is an error and it stuck.
the error that i get is this:
Failed to load resource: the server responded with a status of 500 () from admin-ajax
and the other is:
Uncaught SyntaxError: Unexpected token o in JSON at position 1
from this file:
https://www.mspirit.co.il/wp-admin/options-general.php?page=webp_express_settings_page

how can i fix this?

Thanks