Oracle Enterprise Manager / Cloud Control: Historical Data Not Showing Issue

Problem Description

Last week after one of Oracle Database hosts had to be rebooted because of memory problem. I had the issue with Oracle Enterprise Manager / Cloud Control that historical data of this DB (only for this DB) was not showing any more:

• In "Performance" => "Performance Home" => "View Data: Historical"
  Error Message
  Data Not Available. Statspack data is not available for this database instance. Make sure that Statspack is installed on the target instance.

• In "Performance" => "Top Activity"  => "View Data: Historical"
  Error Message
  (No Data Available)

• In: "Performance"  => "ASH Analytics" in "Top Activity"
  Error
  No useful data was showing

Possible Solution

Completely logout of Enterprise Manager (not only from the DB) and logon back.