For first two scans I was able to get the issues for newly added files and was able to see the modified code in ‘Code’ section. And for later subsequent scans the modified code for files doesn’t get reflected in the ‘Code’ section and I’m also not able to get any new issues or bugs. I’m not sure the sonarqube has scanned the files again.
First of all I would like to stress that I will not be able to deeply investigate your problem since you are on an outdated SonarQube version 7.7 which is neither the 7.9 LTS (Long Term Support) version or the 8.2 LATEST version. I strongly recommend to upgrade to one of those 2 versions
About your problem: What will be reported as new code depends on:
How you have defined the new code period (possibly called Leak period in a couple of places as of 7.7),
What version your provide to SonarQube when you scan (the sonar.projectVersion property, which may be implicit in some cases)
The interval between the different scans you made.