The WriteTag check does not show warnings on tags in eclipse-cs when the severity is set to ignore. This is different behavior compared to the checkstyle CLI:
$ cat Test.java
/**
$ cat config.xml
<module name="Checker">
<property name="charset" value="UTF-8">
<property name="severity" value="warning">
<module name="TreeWalker">
<module name="WriteTag">
<property name="severity" value="ignore">
<property name="tag" value="@author">
<property name="tagFormat" value="\S">
<property name="tagSeverity" value="warning">
<metadata name="net.sf.eclipsecs.core.lastEnabledSeverity" value="warning">
</metadata></property></property></property></property></module>
</module>
</property></property></module>
$ java -jar checkstyle-7.2-all.jar -c config.xml Test.java
Starting audit...
[WARN] C:\cygwin64\home\cpai\work\test\Test.java:3: @author=cpai [WriteTag]
Audit done.
Oops, the Test.java actually looked like:
Not sure how the asterisk disappeared
eclipse-cs uses a checkstyle option to directly exclude ignored modules during configuration loading (https://github.com/checkstyle/checkstyle/blob/master/src/main/java/com/puppycrawl/tools/checkstyle/ConfigurationLoader.java#L178).
This is done to optimize Checkstyle execution within the IDE so that modules are not executed at all if their results would be ignored anyway.
I suppose the WriteTag check was not implemented with that in mind. You should take this up with the Checkstyle core team.
Closing for housekeeping, please take it up with Checkstyle core, if this is still an issue for you.