Below are some more upgrade checklist as shared in the Part 1:
Search 
 | 
 
Run
  a crawl, and review the log files. 
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Run
  search queries, and verify that the queries work as expected and provide
  appropriate results. Twenty-four hours later, view the query reports and look
  for issues. 
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Search
  for people and profiles. 
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Check
  any Search customizations to make sure that they work as expected. 
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My
  Site Web sites 
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Are
  all the Web Parts working? 
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Are
  all features associated with the My Site Web sites working? 
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Can
  users access the sites, or are they seeing "Access Denied" errors? 
 | 
 
If
  the My Site host that they are visiting is not the default My Site host, they
  may see this error. Check that the service application and proxy associations
  are correct, and then check that the My Site host is referenced correctly in
  the User Profile service application. Reset Internet Information Services
  (IIS) to apply any changes. 
 | 
 
User
  Profile, InfoPath and Excel Services 
 | 
 
Are
  they configured correctly? 
 | 
 
Are
  the service application proxies configured the way that you want? 
 | 
 
Do
  you have to create new connections between farms? 
 | 
 
Make
  sure that all existing content such as documents are accessible in the
  upgraded Personal site. 
 | 
 
Check
  all services have administrator permissions or reapply as needed. 
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For
  Excel Services, if using SSS (Secure Store Service) create a new unattended
  service account to interact with Excel Services. 
 | 
 
For
  InfoPath Forms Services, update any links that are used in the upgraded form
  templates by using the Update-SPInfoPathAdminFileURL. 
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