Unable to start confluence after plugin update

[Pandiyan Muthuraman]

Recently upgraded confluence from 6.13.7 to 7.4.1, followed by updated atlassian plugins. After that in a frequent interval of time confleunce service is down.

Here is the log captured in confluence server catalina.out

ErrorHandler to print the first 10 errors. Please call
the 'setErrorHandler' method to fix this.
Error: URI=null Line=1: Document is invalid: no grammar found.
Error: URI=null Line=1: Document root element "atlassian-plugin", must match DOCTYPE root "null".
ESAPI: WARNING: System property [org.owasp.esapi.opsteam] is not set
ESAPI: WARNING: System property [org.owasp.esapi.devteam] is not set
ESAPI: Attempting to load ESAPI.properties via file I/O.
ESAPI: Attempting to load ESAPI.properties as resource file via file I/O.
ESAPI: Not found in 'org.owasp.esapi.resources' directory or file not readable: /home/admin/ESAPI.properties
ESAPI: Not found in SystemResource Directory/resourceDirectory: .esapi/ESAPI.properties
ESAPI: Not found in 'user.home' (/home/admin) directory: /home/admin/esapi/ESAPI.properties
ESAPI: Loading ESAPI.properties via file I/O failed. Exception was: java.io.FileNotFoundException
ESAPI: Attempting to load ESAPI.properties via the classpath.
ESAPI: SUCCESSFULLY LOADED ESAPI.properties via the CLASSPATH from '/ (root)' using class loader for DefaultSecurityConfiguration class!
ESAPI: SecurityConfiguration for Validator.ConfigurationFile.MultiValued not found in ESAPI.properties. Using default: false
ESAPI: SecurityConfiguration for Validator.ConfigurationFile not found in ESAPI.properties. Using default: validation.properties
ESAPI: Attempting to load validation.properties via file I/O.
ESAPI: Attempting to load validation.properties as resource file via file I/O.
ESAPI: Not found in 'org.owasp.esapi.resources' directory or file not readable: /home/admin/validation.properties
ESAPI: Not found in SystemResource Directory/resourceDirectory: .esapi/validation.properties
ESAPI: Not found in 'user.home' (/home/admin) directory: /home/admin/esapi/validation.properties
ESAPI: Loading validation.properties via file I/O failed.
ESAPI: Attempting to load validation.properties via the classpath.
ESAPI: validation.properties could not be loaded by any means. fail.. Caught java.lang.IllegalArgumentException; exception message was: java.lang.IllegalArgumentException: Failed to load ESAPI.properties as a c
lassloader resource.
ESAPI: SecurityConfiguration for ESAPI.printProperties not found in ESAPI.properties. Using default: false
ESAPI: SecurityConfiguration for Encryptor.CipherTransformation not found in ESAPI.properties. Using default: AES/CBC/PKCS5Padding
ESAPI: SecurityConfiguration for ESAPI.Logger not found in ESAPI.properties. Using default: org.owasp.esapi.reference.JavaLogFactory
ESAPI: SecurityConfiguration for Logger.LogApplicationName not found in ESAPI.properties. Using default: true
ESAPI: SecurityConfiguration for Logger.LogServerIP not found in ESAPI.properties. Using default: true
ESAPI: SecurityConfiguration for Logger.ApplicationName not found in ESAPI.properties. Using default: DefaultName
ESAPI: SecurityConfiguration for ESAPI.Logger not found in ESAPI.properties. Using default: org.owasp.esapi.reference.JavaLogFactory
ESAPI: SecurityConfiguration for ESAPI.Logger not found in ESAPI.properties. Using default: org.owasp.esapi.reference.JavaLogFactory
06-Dec-2020 17:35:05.889 INFO [main] org.apache.coyote.AbstractProtocol.start Starting ProtocolHandler ["http-nio-8090"]
06-Dec-2020 17:35:05.905 INFO [main] org.apache.catalina.startup.Catalina.start Server startup in [233,641] milliseconds
06-Dec-2020 17:35:06.753 INFO [http-nio-8090-exec-10] com.sun.jersey.server.impl.application.WebApplicationImpl._initiate Initiating Jersey application, 

To fix temporarily I have cleaned up plugins cache directory

After a week faced same issue and again cleaned up plugins cache. So looking forward permanent solution & root cause ? 

[Nic Brough -Adaptavist-]

These errors make me suspect that you have an invalid app installed.  Clearing the cache was worth a try, but I would go straight to "manage apps" and check through all the installed ones checking for compatibility and updates.

[Pandiyan Muthuraman]

I have checked installed apps under manage apps, all plugins are compatible and updated. But still having this issue in frequent interval 

[Nic Brough -Adaptavist-]

Ok, that was a look at the lines around "atlassian plugin".  The rest of the warnings you have are about it loading defaults because it can't find a setting, they're not indicative of what is failing.  You'll need to look at the rest of the log to see what is stopping it.