Magento – Magento 2.2.6: Error after upgrading to Magento 2.3.0

Just updated from M2.2.6 to M2.3.0, everything seemed to go without a hitch, but after loading the front-end of the website I'm seeing the following error:

Exception #0 (BadMethodCallException): Missing required argument $variablePluginConfigProvider of Magento\Cms\Model\Wysiwyg\CompositeConfigProvider.

Here's the full error:

Exception #0 (BadMethodCallException): Missing required argument 
$variablePluginConfigProvider of 
Magento\Cms\Model\Wysiwyg\CompositeConfigProvider.
#0 C:\xampp\htdocs\m2\vendor\magento\framework\ObjectManager\Factory\Dynamic\Developer.php(34): Magento\Framework\ObjectManager\Factory\AbstractFactory->resolveArgumentsInRuntime('Magento\\Cms\\Mod...', Array, Array)
#1 C:\xampp\htdocs\m2\vendor\magento\framework\ObjectManager\Factory\Dynamic\Developer.php(59): Magento\Framework\ObjectManager\Factory\Dynamic\Developer->_resolveArguments('Magento\\Cms\\Mod...', Array, Array)
#2 C:\xampp\htdocs\m2\vendor\magento\framework\ObjectManager\ObjectManager.php(70): Magento\Framework\ObjectManager\Factory\Dynamic\Developer->create('Magento\\Cms\\Mod...')
#3 C:\xampp\htdocs\m2\vendor\magento\module-cms\Model\Wysiwyg\Config.php(157): Magento\Framework\ObjectManager\ObjectManager->get('Magento\\Cms\\Mod...')
#4 C:\xampp\htdocs\m2\vendor\magento\framework\ObjectManager\Factory\AbstractFactory.php(116): Magento\Cms\Model\Wysiwyg\Config->__construct(Object(Magento\Backend\Model\Url), Object(Magento\Framework\Event\Manager\Proxy), Object(Magento\Framework\Authorization\Interceptor), Object(Magento\Framework\View\Asset\Repository), Object(Magento\Variable\Model\Variable\Config), Object(Magento\Widget\Model\Widget\Config), Object(Magento\Framework\App\Config), Object(Magento\Store\Model\StoreManager), Object(Magento\Framework\Filesystem), Array, Array, NULL)
#5 C:\xampp\htdocs\m2\vendor\magento\framework\ObjectManager\Factory\Dynamic\Developer.php(66): Magento\Framework\ObjectManager\Factory\AbstractFactory->createObject('Magento\\Cms\\Mod...', Array)
#6 C:\xampp\htdocs\m2\vendor\magento\framework\ObjectManager\ObjectManager.php(70): Magento\Framework\ObjectManager\Factory\Dynamic\Developer->create('Magento\\Cms\\Mod...')
#7 C:\xampp\htdocs\m2\vendor\magento\framework\ObjectManager\Factory\AbstractFactory.php(160): Magento\Framework\ObjectManager\ObjectManager->get('Magento\\Cms\\Mod...')
#8 C:\xampp\htdocs\m2\vendor\magento\framework\ObjectManager\Factory\AbstractFactory.php(246): Magento\Framework\ObjectManager\Factory\AbstractFactory->resolveArgument(Array, 'Magento\\Cms\\Mod...', NULL, 'wysiwygConfig', 'Plumrocket\\RMA\\...')
#9 C:\xampp\htdocs\m2\vendor\magento\framework\ObjectManager\Factory\Dynamic\Developer.php(34): Magento\Framework\ObjectManager\Factory\AbstractFactory->resolveArgumentsInRuntime('Plumrocket\\RMA\\...', Array, Array)
#10 C:\xampp\htdocs\m2\vendor\magento\framework\ObjectManager\Factory\Dynamic\Developer.php(59): Magento\Framework\ObjectManager\Factory\Dynamic\Developer->_resolveArguments('Plumrocket\\RMA\\...', Array, Array)
#11 C:\xampp\htdocs\m2\vendor\magento\framework\ObjectManager\ObjectManager.php(70): Magento\Framework\ObjectManager\Factory\Dynamic\Developer->create('Plumrocket\\RMA\\...')
#12 C:\xampp\htdocs\m2\vendor\magento\framework\ObjectManager\Factory\AbstractFactory.php(160): Magento\Framework\ObjectManager\ObjectManager->get('Plumrocket\\RMA\\...')
#13 C:\xampp\htdocs\m2\vendor\magento\framework\ObjectManager\Factory\AbstractFactory.php(246): Magento\Framework\ObjectManager\Factory\AbstractFactory->resolveArgument(Array, 'Plumrocket\\RMA\\...', NULL, 'dataHelper', 'Plumrocket\\RMA\\...')
#14 C:\xampp\htdocs\m2\vendor\magento\framework\ObjectManager\Factory\Dynamic\Developer.php(34): Magento\Framework\ObjectManager\Factory\AbstractFactory->resolveArgumentsInRuntime('Plumrocket\\RMA\\...', Array, Array)
#15 C:\xampp\htdocs\m2\vendor\magento\framework\ObjectManager\Factory\Dynamic\Developer.php(59): Magento\Framework\ObjectManager\Factory\Dynamic\Developer->_resolveArguments('Plumrocket\\RMA\\...', Array, Array)
#16 C:\xampp\htdocs\m2\vendor\magento\framework\ObjectManager\ObjectManager.php(70): Magento\Framework\ObjectManager\Factory\Dynamic\Developer->create('Plumrocket\\RMA\\...')
#17 C:\xampp\htdocs\m2\vendor\magento\framework\Event\ObserverFactory.php(33): Magento\Framework\ObjectManager\ObjectManager->get('Plumrocket\\RMA\\...')
#18 C:\xampp\htdocs\m2\vendor\magento\framework\Event\Invoker\InvokerDefault.php(58): Magento\Framework\Event\ObserverFactory->get('Plumrocket\\RMA\\...')
#19 C:\xampp\htdocs\m2\vendor\magento\framework\Event\Manager.php(66): Magento\Framework\Event\Invoker\InvokerDefault->dispatch(Array, Object(Magento\Framework\Event\Observer))
#20 C:\xampp\htdocs\m2\generated\code\Magento\Framework\Event\Manager\Proxy.php(95): Magento\Framework\Event\Manager->dispatch('view_block_abst...', Array)
#21 C:\xampp\htdocs\m2\vendor\magento\framework\View\Element\AbstractBlock.php(653): Magento\Framework\Event\Manager\Proxy->dispatch('view_block_abst...', Array)
#22 C:\xampp\htdocs\m2\vendor\magento\framework\View\Result\Page.php(249): Magento\Framework\View\Element\AbstractBlock->toHtml()
#23 C:\xampp\htdocs\m2\vendor\magento\framework\View\Result\Layout.php(171): Magento\Framework\View\Result\Page->render(Object(Magento\Framework\App\Response\Http\Interceptor))
#24 C:\xampp\htdocs\m2\vendor\magento\framework\Interception\Interceptor.php(58): Magento\Framework\View\Result\Layout->renderResult(Object(Magento\Framework\App\Response\Http\Interceptor))
#25 C:\xampp\htdocs\m2\vendor\magento\framework\Interception\Interceptor.php(138): Magento\Framework\View\Result\Page\Interceptor->___callParent('renderResult', Array)
#26 C:\xampp\htdocs\m2\vendor\magento\framework\Interception\Interceptor.php(153): Magento\Framework\View\Result\Page\Interceptor->Magento\Framework\Interception\{closure}(Object(Magento\Framework\App\Response\Http\Interceptor))
#27 C:\xampp\htdocs\m2\generated\code\Magento\Framework\View\Result\Page\Interceptor.php(130): Magento\Framework\View\Result\Page\Interceptor->___callPlugins('renderResult', Array, Array)
#28 C:\xampp\htdocs\m2\vendor\magento\framework\App\Http.php(139): Magento\Framework\View\Result\Page\Interceptor->renderResult(Object(Magento\Framework\App\Response\Http\Interceptor))
#29 C:\xampp\htdocs\m2\generated\code\Magento\Framework\App\Http\Interceptor.php(24): Magento\Framework\App\Http->launch()
#30 C:\xampp\htdocs\m2\vendor\magento\framework\App\Bootstrap.php(258): Magento\Framework\App\Http\Interceptor->launch()
#31 C:\xampp\htdocs\m2\index.php(39): Magento\Framework\App\Bootstrap->run(Object(Magento\Framework\App\Http\Interceptor))
#32 {main}

Any ideas what exactly could be missing?