Hi,
My company is using SonarQube of Enterprise Edition Version 7.9.1 (build 27448).
For some PR branch, when using pull request analysis, sonar scanner will scan 0 file. 
here is the 0 scanned log:
I just added a .gitignor with content:
[2020-04-20T05:24:00.946Z] INFO: Load project settings for component key: ‘cas-system-python-lib’
[2020-04-20T05:24:01.201Z] INFO: Load project settings for component key: ‘cas-system-python-lib’ (done) | time=147ms
[2020-04-20T05:24:01.201Z] INFO: Load project branches
[2020-04-20T05:24:01.456Z] INFO: Load project branches (done) | time=153ms
[2020-04-20T05:24:01.456Z] INFO: Load project pull requests
[2020-04-20T05:24:01.712Z] INFO: Load project pull requests (done) | time=149ms
[2020-04-20T05:24:01.712Z] INFO: Load branch configuration
[2020-04-20T05:24:01.712Z] INFO: Load branch configuration (done) | time=9ms
[2020-04-20T05:24:01.712Z] INFO: Load quality profiles
[2020-04-20T05:24:01.973Z] INFO: Load quality profiles (done) | time=219ms
[2020-04-20T05:24:01.973Z] INFO: Detected Jenkins
[2020-04-20T05:24:01.973Z] INFO: Load active rules
[2020-04-20T05:24:08.503Z] INFO: Load active rules (done) | time=6590ms
[2020-04-20T05:24:08.503Z] INFO: Pull request 100 for merge into master from feature/CAS-32942
[2020-04-20T05:24:08.503Z] INFO: SCM collecting changed files in the branch
[2020-04-20T05:24:08.760Z] INFO: SCM collecting changed files in the branch (done) | time=185ms
[2020-04-20T05:24:09.017Z] INFO: Indexing files…
[2020-04-20T05:24:09.017Z] INFO: Project configuration:
[2020-04-20T05:24:09.017Z] INFO: Excluded sources for coverage: /tests/, **/setup.py, **/init.py, **/README.md
[2020-04-20T05:24:09.277Z] INFO: 0 files indexed
[2020-04-20T05:24:09.277Z] INFO: 0 files ignored because of scm ignore settings
[2020-04-20T05:24:09.277Z] INFO: ------------- Run sensors on module cas-system-python-lib
[2020-04-20T05:24:09.839Z] INFO: Load metrics repository
[2020-04-20T05:24:09.839Z] INFO: Load metrics repository (done) | time=146ms
[2020-04-20T05:24:11.204Z] INFO: Load server rules
[2020-04-20T05:24:12.570Z] INFO: Load server rules (done) | time=1094ms
[2020-04-20T05:24:15.089Z] INFO: Sensor Embedded CSS Analyzer Sensor [css]
[2020-04-20T05:24:15.345Z] INFO: 0 source files to be analyzed
[2020-04-20T05:24:15.345Z] INFO: 0/0 source files have been analyzed
[2020-04-20T05:24:15.345Z] INFO: Sensor Embedded CSS Analyzer Sensor [css] (done) | time=182ms
[2020-04-20T05:24:15.345Z] INFO: Sensor JavaXmlSensor [java]
[2020-04-20T05:24:15.345Z] INFO: Sensor JavaXmlSensor [java] (done) | time=1ms
[2020-04-20T05:24:15.345Z] INFO: Sensor OWASP Zap-Check [zap]
[2020-04-20T05:24:15.345Z] INFO: Process ZAP report
[2020-04-20T05:24:15.345Z] WARN: ZAP report does not exist.
[2020-04-20T05:24:15.345Z] INFO: Process ZAP report (done) | time=0ms
[2020-04-20T05:24:15.345Z] INFO: Sensor OWASP Zap-Check [zap] (done) | time=1ms
[2020-04-20T05:24:15.345Z] INFO: Sensor JaCoCo XML Report Importer [jacoco]
[2020-04-20T05:24:15.345Z] INFO: Sensor JaCoCo XML Report Importer [jacoco] (done) | time=2ms
[2020-04-20T05:24:15.345Z] INFO: Sensor JavaSecuritySensor [security]
here is the normal log
[2020-04-15T16:12:56.756Z] INFO: Load project settings for component key: ‘cas-system-python-lib’
[2020-04-15T16:12:56.756Z] INFO: Load project settings for component key: ‘cas-system-python-lib’ (done) | time=149ms
[2020-04-15T16:12:56.756Z] INFO: Load project branches
[2020-04-15T16:12:57.012Z] INFO: Load project branches (done) | time=148ms
[2020-04-15T16:12:57.012Z] INFO: Load project pull requests
[2020-04-15T16:12:57.012Z] INFO: Load project pull requests (done) | time=144ms
[2020-04-15T16:12:57.012Z] INFO: Load branch configuration
[2020-04-15T16:12:57.012Z] INFO: Load branch configuration (done) | time=2ms
[2020-04-15T16:12:57.012Z] INFO: Load quality profiles
[2020-04-15T16:12:57.269Z] INFO: Load quality profiles (done) | time=186ms
[2020-04-15T16:12:57.269Z] INFO: Detected Jenkins
[2020-04-15T16:12:57.269Z] INFO: Load active rules
[2020-04-15T16:13:03.805Z] INFO: Load active rules (done) | time=6590ms
[2020-04-15T16:13:04.060Z] INFO: Pull request 99 for merge into master from feature/CAS-32798
[2020-04-15T16:13:04.060Z] INFO: SCM collecting changed files in the branch
[2020-04-15T16:13:04.060Z] INFO: SCM collecting changed files in the branch (done) | time=113ms
[2020-04-15T16:13:04.316Z] INFO: Indexing files…
[2020-04-15T16:13:04.316Z] INFO: Project configuration:
[2020-04-15T16:13:04.316Z] INFO: Excluded sources for coverage: /tests/, **/setup.py, **/init.py, **/README.md
[2020-04-15T16:13:04.573Z] INFO: 127 files indexed
[2020-04-15T16:13:04.573Z] INFO: 0 files ignored because of scm ignore settings
[2020-04-15T16:13:04.573Z] INFO: Quality profile for py: Sonar way
[2020-04-15T16:13:04.573Z] INFO: Quality profile for xml: Sonar way
[2020-04-15T16:13:04.573Z] INFO: Quality profile for yaml: Sonar way
[2020-04-15T16:13:04.573Z] INFO: ------------- Run sensors on module cas-system-python-lib
[2020-04-15T16:13:04.573Z] INFO: Load metrics repository
[2020-04-15T16:13:04.831Z] INFO: Load metrics repository (done) | time=176ms
[2020-04-15T16:13:05.760Z] INFO: Load server rules
[2020-04-15T16:13:07.129Z] INFO: Load server rules (done) | time=1270ms
[2020-04-15T16:13:09.021Z] INFO: Sensor Embedded CSS Analyzer Sensor [css]
[2020-04-15T16:13:09.021Z] INFO: 0 source files to be analyzed
[2020-04-15T16:13:09.021Z] INFO: Sensor Embedded CSS Analyzer Sensor [css] (done) | time=64ms
[2020-04-15T16:13:09.021Z] INFO: 0/0 source files have been analyzed
[2020-04-15T16:13:09.021Z] INFO: Sensor JavaXmlSensor [java]
[2020-04-15T16:13:09.021Z] INFO: 3 source files to be analyzed
[2020-04-15T16:13:09.276Z] INFO: 3/3 source files have been analyzed
[2020-04-15T16:13:09.276Z] INFO: Sensor JavaXmlSensor [java] (done) | time=253ms
[2020-04-15T16:13:09.276Z] INFO: Sensor XML Sensor [xml]
[2020-04-15T16:13:09.276Z] INFO: 3 source files to be analyzed
[2020-04-15T16:13:09.533Z] WARN: Unable to analyse file file:///var/lib/jenkins/workspace/cas-system-python-lib_PR-99/pylint-report.xml;
[2020-04-15T16:13:09.533Z] INFO: 3/3 source files have been analyzed
Thanks/Sai
Thanks/Sai