I found the solution for me!
This bypasses the problem with the certificate Lets Encrypt.
This should work for you:
1 – Change your wp-config.phh file by adding the following formula:
define ( ‘ALTERNATE_WP_CRON’, true);
2 – Change your .htaccess file
RewriteEngine On
RewriteRule * – [E = noabort: 1].
RewriteRule * – [E = noconntimeout: 1].
3 – In the BACKWPUP plugin parameter then go to “Operations” and to “maximun time of execution” to 0.
After several hours, this to work for me … ??