Zend certified PHP/Magento developer

Magento 2.3.4 error after setup:upgrade command

Fatal error: Uncaught ReflectionException: Class MagentoFrameworkAppResourceConnectionProxy does not exist in /var/www/html/magento2/vendor/magento/framework/Code/Reader/ClassReader.php:26 Stack trace: #0 /var/www/html/magento2/vendor/magento/framework/Code/Reader/ClassReader.php(26): ReflectionClass->__construct('Magento\Framewo...') #1 /var/www/html/magento2/vendor/magento/framework/ObjectManager/Definition/Runtime.php(54): MagentoFrameworkCodeReaderClassReader->getConstructor('Magento\Framewo...') #2 /var/www/html/magento2/vendor/magento/framework/ObjectManager/Factory/Dynamic/Developer.php(48): MagentoFrameworkObjectManagerDefinitionRuntime->getParameters('Magento\Framewo...') #3 /var/www/html/magento2/vendor/magento/framework/ObjectManager/ObjectManager.php(70): MagentoFrameworkObjectManagerFactoryDynamicDeveloper->create('Magento\Framewo...') #4 /var/www/html/magento2/vendor/magento/framework/ObjectManager/Factory/AbstractFactory.php(167): MagentoFrameworkObjectManagerObjectManager->get('Mage in /var/www/html/magento2/vendor/magento/framework/Code/Reader/ClassReader.php on line 26

Everytime I use command:

bin/magento setup:upgrade

I had the error. After this command I use:

bin/magento setup:di:compile
bin/magento setup:static-content:deploy -f
bin/magento cache:flush

And site is working again.
Magento 2.3.4 installed on VPS server 4GB RAM, 50GB SSD. System is Ubuntu 18.04 using Nginx and Percona 5.7 and Elasticsearch 6.8.8 on same server. My php.ini configuration:

memory_limit = 2G

max_execution_time = 3600

max_input_time = 1800

upload_max_filesize = 10M

zlib.output_compression = On

I am using developer mode in Magento 2.3.4. What Can I check ? I installed CustomChekout module, and on this VPS serwer got error:

knockout.js:3381 Uncaught TypeError: Unable to process binding "foreach: function(){return {data:currentBillingAddress().customAttributes,as:'element'} }"
Message: Unable to process binding "text: function(){return $parent.getCustomAttributeLabel(element) }"
Message: Cannot read property 'customer-email' of undefined

at UiClass.getCustomAttributeLabel (billing-address.js:258)
at text (eval at createBindingsStringEvaluator (knockout.js:2982), :3:72)
at update (knockout.js:4659)
at ko.dependentObservable.disposeWhenNodeIsRemoved (knockout.js:3373)
at Function.evaluateImmediate_CallReadThenEndDependencyDetection (knockout.js:2173)
at Function.evaluateImmediate_CallReadWithDependencyDetection (knockout.js:2140)
at Function.evaluateImmediate (knockout.js:2101)
at Object.ko.computed.ko.dependentObservable (knockout.js:1954)
at knockout.js:3371
at Object.arrayForEach (knockout.js:159)

Where could be a problem ?