Hello @andrzejs,
As you mentioned in your post, speed of analysis was expected to take a toll as of version 6 of the Java analyzer.
While the performance degradation has been tamed, the analyzer is still expected to be slower on version 6.3 and greater than it was on version 5.
Has there been any change in your infrastructure as you moved to SonarQube 8.9.2?
Dorian