Emails and Contacts sections suddenly inaccessible

Your software
My Mautic version is: 2.15.3
My PHP version is: 7.2.24

Your problem
Parts of Mautic down/inaccessible - ‘Emails’ and ‘Contacts’ in particular. No problems accessing other sections like ‘Companies’, ‘Segments’, etc. Errors in the log.

I have actively used this Mautic installation all year without problems. This week emails were not going out even though Mautic said they did, in hindsight probably caused by php memory limits that were suddenly lowered on the server. The recent upgrade from 2.15.2 to 2.15.3 could be a factor as well.

These errors are showing in the log:

[2019-11-16 10:23:32] mautic.WARNING: PHP Warning - require(/home/bizpartn/public_html/mrktng/app/cache/prod/doctrine/orm/Proxies/__CG__MauticCategoryBundleEntityCategory.php): failed to open stream: No such file or directory - in file /home/bizpartn/public_html/mrktng/vendor/doctrine/common/lib/Doctrine/Common/Proxy/AbstractProxyFactory.php - at line 209 {“className”:“Mautic\CategoryBundle\Entity\Category”,“classMetadata”:"[object] (Doctrine\ORM\Mapping\ClassMetadata: Doctrine\ORM\Mapping\ClassMetadataInfo@0000000039b50175000000005cb62ba3)",“proxyClassName”:“Proxies\CG\Mautic\CategoryBundle\Entity\Category”,“fileName”:“public_html/mrktng/app/cache/prod/doctrine/orm/Proxies/__CG__MauticCategoryBundleEntityCategory.php”}
[2019-11-16 10:23:32] mautic.WARNING: PHP Warning - require(/public_html/mrktng/app/cache/prod/doctrine/orm/Proxies/__CG__MauticCategoryBundleEntityCategory.php): failed to open stream: No such file or directory - in file /public_html/mrktng/vendor/doctrine/common/lib/Doctrine/Common/Proxy/AbstractProxyFactory.php - at line 209 {“className”:“Mautic\CategoryBundle\Entity\Category”,“classMetadata”:"[object] (Doctrine\ORM\Mapping\ClassMetadata: Doctrine\ORM\Mapping\ClassMetadataInfo@0000000039b50175000000005cb62ba3)",“proxyClassName”:“Proxies\CG\Mautic\CategoryBundle\Entity\Category”,“fileName”:"/public_html/mrktng/app/cache/prod/doctrine/orm/Proxies/__CG__MauticCategoryBundleEntityCategory.php"}
[2019-11-16 10:23:32] mautic.ERROR: PHP Notice: require(): Failed opening required ‘/public_html/mrktng/app/cache/prod/doctrine/orm/Proxies/__CG__MauticCategoryBundleEntityCategory.php’ (include_path=’.:/opt/cpanel/ea-php72/root/usr/share/pear’) - in file /public_html/mrktng/vendor/doctrine/common/lib/Doctrine/Common/Proxy/AbstractProxyFactory.php - at line 209
[2019-11-16 10:23:32] mautic.ERROR: Symfony\Component\Debug\Exception\FatalErrorException: Notice: require(): Failed opening required ‘/public_html/mrktng/app/cache/prod/doctrine/orm/Proxies/__CG__MauticCategoryBundleEntityCategory.php’ (include_path=’.:/opt/cpanel/ea-php72/root/usr/share/pear’) - in file /public_html/mrktng/vendor/doctrine/common/lib/Doctrine/Common/Proxy/AbstractProxyFactory.php - at line 209
[2019-11-16 10:23:32] mautic.CRITICAL: Uncaught PHP Exception Symfony\Component\Debug\Exception\FatalErrorException: “Compile Error: require(): Failed opening required ‘/public_html/mrktng/app/cache/prod/doctrine/orm/Proxies/__CG__MauticCategoryBundleEntityCategory.php’ (include_path=’.:/opt/cpanel/ea-php72/root/usr/share/pear’)” at /public_html/mrktng/vendor/doctrine/common/lib/Doctrine/Common/Proxy/AbstractProxyFactory.php line 209 {“exception”:"[object] (Symfony\Component\Debug\Exception\FatalErrorException(code: 0): Compile Error: require(): Failed opening required ‘/public_html/mrktng/app/cache/prod/doctrine/orm/Proxies/__CG__MauticCategoryBundleEntityCategory.php’ (include_path=’.:/opt/cpanel/ea-php72/root/usr/share/pear’) at /public_html/mrktng/vendor/doctrine/common/lib/Doctrine/Common/Proxy/AbstractProxyFactory.php:209)"}

Steps I have tried to fix the problem:

Nothing yet. Not sure where to start. I had been trying to fix the mailings problem, by clearing caches etc. I may have messed something up with an SSH command? I now want to avoid making things worse…

Nevermind. I think fixing the database schema by running /s/update/schema from the browser address bar fixed the problem.

And last weeks mailing has suddenly gone out - lesson: too low php memory limit can block your emails going out, even if Mautic says they have been sent.

Other clever observations about the reported errors welcome.