maven clean plugin fails

Question

I use maven 3.8.4 and have my clean plugin configured like that:

            <plugin>
                <artifactId>maven-clean-plugin</artifactId>
                <version>3.2.0</version>
                <configuration>
                    <filesets>
                        <fileset>
                            <directory>src/site/tex</directory>
                            <includes>
                                <include>buildParams.tex</include>
                            </includes>
                        </fileset>
                        <fileset>
                            <directory>src/test/resources/integration</directory>
                            <includes>
                                <include>pom4pdf.xml</include>
                            </includes>
                        </fileset>
                    </filesets>
                </configuration>
            </plugin>

Without any errors, mvn clean just does not clean the given files. I also tried with mvn clean -X which yields

...
[INFO] Deleting file /home/ernst/OpenSource/LatexMavenPluginGit/maven-latex-plugin/maven-latex-plugin/src/site/tex/buildParams.tex
...
[INFO] Deleting /home/ernst/OpenSource/LatexMavenPluginGit/maven-latex-plugin/maven-latex-plugin/src/test/resources/integration (includes = [pom4pdf.xml], excludes = [])
[INFO] Deleting file /home/ernst/OpenSource/LatexMavenPluginGit/maven-latex-plugin/maven-latex-plugin/src/test/resources/integration/pom4pdf.xml

Well all seems ok, but still the files remain at place. What is a bit risky but seems unrelated tome, that are the warnings from vscode

Build path specifies execution environment JavaSE-1.8. There are no JREs installed in the workspace that are strictly compatible with this environment. 
The compiler compliance specified is 1.8 but a JRE 11 is used

I cannot remove those easily.

Help very much appreciated. It seems to me that clean did work some time. I try workaround: .gitignore.