Cron fails on WHMCS Updates (8.12.1)

[Koboh]

Hello,

I have recently updated to 8.12 and noticed my daily cron is not completing. I have updated to 8.12.1 just in case one of the maintenance fixes would help but it is still failing.

When manually forcing the cron in the command line I can see it reaches 32/36 WHMCS Updates and provides this error:

PHP Fatal error:  Declaration of WHMCS\Installer\Composer\WhmcsComposerApplication::getComposer($required = , $disablePlugins = ) must be compatible with Composer\Console\Application::getComposer(bool $required = true, ?bool $disablePlugins = null, ?bool $disableScripts = null): ?Composer\Composer in unknown on line 0
[WHMCS Application] ERROR: Whoops\Exception\ErrorException: Declaration of WHMCS\Installer\Composer\WhmcsComposerApplication::getComposer($required = , $disablePlugins = ) must be compatible with Composer\Console\Application::getComposer(bool $required = true, ?bool $disablePlugins = null, ?bool $disableScripts = null): ?Composer\Composer in unknown:0 Stack trace: #0 /var/www/whmcs/vendor/whmcs/whmcs-foundation/lib/Utility/Error/Run.php(0): WHMCS\Utility\Error\Run->handleError() #1 [internal function]: WHMCS\Utility\Error\Run->handleShutdown() #2 {main} {"exception":"[object] (Whoops\\Exception\\ErrorException(code: 64): Declaration of WHMCS\\Installer\\Composer\\WhmcsComposerApplication::getComposer($required = , $disablePlugins = ) must be compatible with Composer\\Console\\Application::getComposer(bool $required = true, ?bool $disablePlugins = null, ?bool $disableScripts = null): ?Composer\\Composer at unknown:0)"} []
Whoops\Exception\ErrorException: Declaration of WHMCS\Installer\Composer\WhmcsComposerApplication::getComposer($required = , $disablePlugins = ) must be compatible with Composer\Console\Application::getComposer(bool $required = true, ?bool $disablePlugins = null, ?bool $disableScripts = null): ?Composer\Composer in unknown:0

#0 /var/www/whmcs/vendor/whmcs/whmcs-foundation/lib/Utility/Error/Run.php(0): WHMCS\Utility\Error\Run->handleError()
#1 [internal function]: WHMCS\Utility\Error\Run->handleShutdown()
#2 {main}

Has anyone seen this and are you able to help me resolve it, please?

[Bezerra]

I'm having the same problem here. Has anyone managed to solve it?

[wtools]

You had deleted the old vendor folder and then used the latest vendor folder? 
Also you had updated your composer version?