Supposedly due to failed tests:

Email was triggered for: Unstable (Test Failures)
Email was triggered for: Unstable (Test Failures) - 1st
Trigger Unstable (Test Failures) was overridden by another trigger and will not send an email.
Trigger Status Changed was overridden by another trigger and will not send an email.
Sending email for trigger: Unstable (Test Failures) - 1st
Sending email to: build@tigase.net support+tigase-server@tigase.com
Triggering a new build of multijob
Finished: UNSTABLE

But neither upstream jobs are unstable:

Waiting for the completion of tigase-projects-parent
tigase-projects-parent #88 completed. Result was SUCCESS
Build step 'Trigger/call builds on other projects' changed build result to SUCCESS
Waiting for the completion of tigase-utils
tigase-utils #2660 completed. Result was SUCCESS
Waiting for the completion of tigase-server-stable
tigase-server-stable #853 completed. Result was SUCCESS

nor there are failed tests:

[INFO] Tests run: 248, Failures: 0, Errors: 0, Skipped: 0

Upon further investigation it looks like problem with jenkins itself and it's trying to parse results:

	Test Result (7 failures / ±0)

    TEST-tigase.annotations.DeprecationTest.xml.[failed-to-read]
    TEST-tigase.cluster.api.ClusterElementTest.xml.[failed-to-read]
    TEST-tigase.db.jdbc.JDBCRepositoryTest.xml.[failed-to-read]
    TEST-tigase.server.BootstrapTest.xml.[failed-to-read]
    TEST-tigase.server.amp.db.JDBCMsgBroadcastRepositoryTest.xml.[failed-to-read]
    TEST-tigase.server.amp.db.JDBCMsgRepositoryTest.xml.[failed-to-read]
    TEST-tigase.util.updater.UpdatesCheckerTest.xml.[failed-to-read]

Because of nested XML, which is just typical output of junit:

Failed to read test report file /var/lib/jenkins/jobs/tigase-server/workspace/target/surefire-reports/TEST-tigase.annotations.DeprecationTest.xml
org.dom4j.DocumentException: Error on line 65 of document  : XML document structures must start and end within the same entity. Nested exception: XML document structures must start and end within the same entity.

  <testcase name="test" classname="tigase.annotations.DeprecationTest" time="0.316">
    <failure message="Class class tigase.auth.impl.AuthRepoPlainCallbackHandler should be removed in this version, deprecated since 8.0.0&#10;Expected: version bigger than &lt;8.1.0&gt;&#10;     but: was &lt;8.1.0&gt;"

When run from console this is reported in console as warning hence overlooked:

[WARNING] ForkStarter IOException: org.apache.maven.surefire.report.SafeThrowable.<init>(Ljava/lang/String;)V
org.apache.maven.surefire.report.SafeThrowable.<init>(Ljava/lang/String;)V
org.apache.maven.surefire.report.SafeThrowable.<init>(Ljava/lang/String;)V
org.apache.maven.surefire.report.SafeThrowable.<init>(Ljava/lang/String;)V
org.apache.maven.surefire.report.SafeThrowable.<init>(Ljava/lang/String;)V
org.apache.maven.surefire.report.SafeThrowable.<init>(Ljava/lang/String;)V
org.apache.maven.surefire.report.SafeThrowable.<init>(Ljava/lang/String;)V. See the dump file /var/lib/jenkins/jobs/tigase-server/workspace/target/surefire-reports/2019-03-04T02-56-10_784-jvmRun1.dumpstream

@andrzej.wojcik while working on it I realised that there is a small issue with the deprecationTest - it was marking members for removal with next minor version (which shouldn't be the case). I adjusted the test for the next major version (which is what we agreed before) and removed members accordingly.

(I understand the idea - some of them are quite ancient and we should remove them, but IMHO we should stick to "remove in next major version" to avoid more confusion)