Don't know if it's related at all, but I had the same error when viewing certain pages since the upgrade and traced it down to my custonisations of date outputs in e.g. the Page List block. I wanted just the month and year to be displayed so I'd made the following change to a new template based on view.php:



This no longer works, seemingly getLocalDateTime is gone. I've recreated my custom template and changed the affected edit to:



Now it's fine for me

Error thrown with message "Class 'Concrete\Core\Localization\Service\Config' not found"

Stacktrace:
#24 Error in /var/www/htm/releases/1561583979/public/concrete/src/Localization/Service/Date.php:929
#23 Concrete\Core\Localization\Service\Date:getSystemDateTime in /var/www/htm/releases/1561583979/public/packages/core/themes/edu/file.php:12
#22 include in /var/www/htm/releases/1561583979/public/concrete/src/View/View.php:288
#21 Concrete\Core\View\View:renderTemplate in /var/www/htm/releases/1561583979/public/concrete/src/View/View.php:250
#20 Concrete\Core\View\View:renderViewContents in /var/www/htm/releases/1561583979/public/concrete/src/View/AbstractView.php:164
#19 Concrete\Core\View\AbstractView:render in /var/www/htm/releases/1561583979/public/concrete/src/Http/ResponseFactory.php:148
#18 Concrete\Core\Http\ResponseFactory:view in /var/www/htm/releases/1561583979/public/concrete/src/Http/ResponseFactory.php:215
#17 Concrete\Core\Http\ResponseFactory:controller in /var/www/htm/releases/1561583979/public/concrete/src/Http/ResponseFactory.php:362
#16 Concrete\Core\Http\ResponseFactory:collection in /var/www/htm/releases/1561583979/public/concrete/src/Http/DefaultDispatcher.php:134
#15 Concrete\Core\Http\DefaultDispatcher:handleDispatch in /var/www/htm/releases/1561583979/public/concrete/src/Http/DefaultDispatcher.php:58
#14 Concrete\Core\Http\DefaultDispatcher:dispatch in /var/www/htm/releases/1561583979/public/concrete/src/Http/Middleware/DispatcherDelegate.php:39
#13 Concrete\Core\Http\Middleware\DispatcherDelegate:next in /var/www/htm/releases/1561583979/public/concrete/src/Http/Middleware/ThumbnailMiddleware.php:76
#12 Concrete\Core\Http\Middleware\ThumbnailMiddleware:process in /var/www/htm/releases/1561583979/public/concrete/src/Http/Middleware/MiddlewareDelegate.php:50
#11 Concrete\Core\Http\Middleware\MiddlewareDelegate:next in /var/www/htm/releases/1561583979/public/concrete/src/Http/Middleware/FrameOptionsMiddleware.php:39
#10 Concrete\Core\Http\Middleware\FrameOptionsMiddleware:process in /var/www/htm/releases/1561583979/public/concrete/src/Http/Middleware/MiddlewareDelegate.php:50
#9 Concrete\Core\Http\Middleware\MiddlewareDelegate:next in /var/www/htm/releases/1561583979/public/concrete/src/Http/Middleware/CookieMiddleware.php:35
#8 Concrete\Core\Http\Middleware\CookieMiddleware:process in /var/www/htm/releases/1561583979/public/concrete/src/Http/Middleware/MiddlewareDelegate.php:50
#7 Concrete\Core\Http\Middleware\MiddlewareDelegate:next in /var/www/htm/releases/1561583979/public/concrete/src/Http/Middleware/ApplicationMiddleware.php:29
#6 Concrete\Core\Http\Middleware\ApplicationMiddleware:process in /var/www/htm/releases/1561583979/public/concrete/src/Http/Middleware/MiddlewareDelegate.php:50
#5 Concrete\Core\Http\Middleware\MiddlewareDelegate:next in /var/www/htm/releases/1561583979/public/concrete/src/Http/Middleware/MiddlewareStack.php:86
#4 Concrete\Core\Http\Middleware\MiddlewareStack:process in /var/www/htm/releases/1561583979/public/concrete/src/Http/DefaultServer.php:85
#3 Concrete\Core\Http\DefaultServer:handleRequest in /var/www/htm/releases/1561583979/public/concrete/src/Foundation/Runtime/Run/DefaultRunner.php:119
#2 Concrete\Core\Foundation\Runtime\Run\DefaultRunner:run in /var/www/htm/releases/1561583979/public/concrete/src/Foundation/Runtime/DefaultRuntime.php:102
#1 Concrete\Core\Foundation\Runtime\DefaultRuntime:run in /var/www/htm/releases/1561583979/public/concrete/dispatcher.php:36
#0 require in /var/www/htm/releases/1561583979/public/index.php:3

as derykmarl wrote, look for
$date = $dh->getLocalDateTime($page->getCollectionDatePublic(), 'F Y');
in your theme of blocks in the application folder.

Fixing these entries will solve your problem. For some reason, the date fix was not working for me

I just removed the code as it was no longer needed. I was then able to update to 5.8.5

Thanks, wavemedia. Actually I did that, but I wanted to confirm the bug because the method is marked as deprecated, but it should continue to work until the next major version. It looks like the root cause here is that something still in the core is still relying on the method, so it does need to be fixed in the core.