Site down with "Cannot autowire service...references class "Mautic\CoreBundle\Helper\ComposerHelper" but no such service exists."

Product Support
1

Your software
My Mautic version is: Whatever the previous update was as of 3/14/22. I was going to attempt the latest update this morning when I found my installation down.
My PHP version is: 7.4
My Database type and version is: MariaDB (MySQL) 5.6.43

Your problem
Installation worked last night and I sent out a newsletter. This morning I get " The site is currently offline due to encountering an error. If the problem persists, please contact the system administrator."

These errors are showing in the log:
[16-Mar-2022 15:26:15 UTC] Symfony\Component\DependencyInjection\Exception\RuntimeException: Cannot autowire service “Mautic\MarketplaceBundle\Command\InstallCommand”: argument “$composer” of method “__construct()” references class “Mautic\CoreBundle\Helper\ComposerHelper” but no such service exists. - in file /home/cstukfps/email/vendor/symfony/dependency-injection/Compiler/DefinitionErrorExceptionPass.php - at line 54

Steps I have tried to fix the problem:
I’ve manually deleted the cache through Cpanel and tried using terminal to reset file permissions as per a post on the Mautic website. I also tried starting the next update, but that gives the same error:

$ php bin/console mautic:update:find

In DefinitionErrorExceptionPass.php line 54:

Cannot autowire service “Mautic\MarketplaceBundle\Command\InstallCommand”: argument “$composer” of method “__construct()” references class “Mautic\CoreBundle\Helper\ComposerHelper” but no such service exists."

The ComposerHelper.pgp its referring to exists, through the path on my installation is email\app\bundles\CoreBundle\Helper\ComposerHelper

2

We do not yet support PHP8. Please drop it to 7.4.

Maybe your host updated PHP without you knowing?

3

Hmm. Maybe. That is indeed weird.

However, I set it back down to 7.4, deleted the cache and browser data, and still get the same error.
Earlier, I ran the following, was any of this wrong?

find . -type f -not -perm 644 -exec chmod 644 {} +
find . -type d -not -perm 755 -exec chmod 755 {} +
chmod -R g+w var/cache/ var/logs/ app/config/
chmod -R g+w media/files/ media/images/ translations/
rm -rf var/cache/*

chown -R cstukfps:cstukfps /home/cstukfps/email  (where cstukfps is obviously my installation, user, and permissions group name).
4

Interestringly, when I look at app\bundles\MarketplaceBundle\Command\InstallCommand , I see a syntax error on the line:

private ComposerHelper $composer;

It says "unexpected t_string, expected t_function or t_const