After upgrading Jenkins LTS version from 1.651.1 to 2.7.1 we have nearly all builds hanging. Some of them hanging in "Before Build" phase and some are seem to be finished but hanging also.

For example the output for a hanging build in "before build" phase:

[EnvInject] - Variables injected successfully.
Email was triggered for: Before Build
Sending email for trigger: Before Build

And an example about the "finished build" phase:

[INFO] BUILD SUCCESS
[INFO] ------------------------------------------------------------------------
[INFO] Total time: 01:33 min
[INFO] Finished at: 2016-07-22T10:34:15+02:00
[INFO] Final Memory: 71M/809M
[INFO] ------------------------------------------------------------------------
Waiting for Jenkins to finish collecting data
channel stopped
Java HotSpot(TM) 64-Bit Server VM warning: ignoring option PermSize=128m; support was removed in 8.0
Java HotSpot(TM) 64-Bit Server VM warning: ignoring option MaxPermSize=256m; support was removed in 8.0

We guess it is a general problem with jenkins master/node .. nothing plugin specific. But for example builds with simple scripts (powershell) working and sending emails (so not email-ext specific) and some builds are finishing after a great period of time.

We have no clue which circumstances making this behavior.

We have also seen this after trying to upgrade LTS from 1.651.1 to 1.651.2 .. so possible some changes between those versions making the difference.