Same here, we're seeing this since the last updates. Most projects are pipelines as well. Right after starting (and probably before the pipeline really starts), the ETA is displayed. However, shortly afterwards and until the build is completely finished, the time isn't here anymore:
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According to https://groups.google.com/forum/#!topic/jenkinsci-users/BdKmRrkjir4 the bug is very easy to fix:
Resetting the executableEstimatedDuration only when there is no asynchrounous execution seems to solve the problem. So the resulting Code in hudson.model.Executor is
[...]
458 } finally {
459 if (asynchronousExecution == null) {
460 finish2();
461 executableEstimatedDuration = DEFAULT_ESTIMATED_DURATION;
462 }
463 }
[...]
Please provide more info about the issue: Job types you use, UI screenshots, etc.