Ok, I got it again, this time when using gradle (m6/7) with Jenkins (as user jenkins) which most likely lacks some system linux requirements and causes the build to succeed with a failure, which is quite inconvenient as jenkins will recognize this as failed built....
fyi: notify-send is installed

16:14:14.892 [DEBUG] [org.gradle.process.internal.ProcessBuilderFactory] creating process builder for command '/usr/bin/notify-send'
16:14:14.892 [DEBUG] [org.gradle.process.internal.ProcessBuilderFactory] in directory /var/lib/jenkins/workspace/mopay20
16:14:14.893 [DEBUG] [org.gradle.process.internal.ProcessBuilderFactory] with argument#0 = Build successful
16:14:14.893 [DEBUG] [org.gradle.process.internal.ProcessBuilderFactory] with argument#1 = 12 tasks executed
16:14:14.926 [DEBUG] [org.gradle.process.internal.DefaultExecHandle] Started command '/usr/bin/notify-send'.
16:14:14.975 [ERROR] [system.err]
16:14:14.976 [ERROR] [system.err] GLib-GObject-CRITICAL **: g_object_unref: assertion `G_IS_OBJECT (object)' failed
16:14:14.976 [ERROR] [system.err] aborting...
16:14:14.976 [DEBUG] [org.gradle.process.internal.DefaultExecHandle] Process finished for command '/usr/bin/notify-send'.
16:14:14.982 [ERROR] [org.gradle.BuildExceptionReporter]
16:14:14.982 [ERROR] [org.gradle.BuildExceptionReporter] FAILURE: Build failed with an exception.

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