If you are not have any integration & not using cloud services then disable the ServicesStatisticsJob by "unbind" the configuration of the service with PID com.day.cq.wcm.webservicesupport.impl.statistics.ServicesStatisticsJobYou can reach the configuration directly at this URL.http://HOST:PORT/syst...

Sounds like when you upgraded to 5.5 [1] might not tested your application correctly.  Engage with official support channel so that your history of instance can be discussed to arrive for possible solution.[1]   https://helpx.adobe.com/experience-manager/kb/replication-privileges-missing-after-upgra...

File an official support request with below information*)   Is it cluster setup*)   Complete log files*)   Output of /system/console/bundles/.json

Not sure which version you are referring here.   AFAIK latest aem does not use underscore instead lodash.

https://helpx.adobe.com/experience-manager/kb/workflow-monitor-via-jmx.html

Yes crypto token avoids to use sticky issue.  Note http Sessions are server side sessions and hence violate the sessionless principle of REST and therefore should be used with care.  Crypto token will  not solve http session for that you need to depond on application server.   In aem with the defaul...

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Use Closed user group. https://docs.adobe.com/docs/en/aem/6-0/administer/security/cug.html

Refer https://helpx.adobe.com/aem-forms/6/getting-started.html

Install the hotfix 6760 and verify. Otherwise file a support request.