Major Issue
When creating plugins that handle node availability it is necessary to access a node's temporaryOfflineCause so that it can be examined (e.g. to find out which user set it etc.).
This can be easily done if the node is still connected (== still has a channel) but if another OfflineCause is set (e.g. because of a connection termination) it is impossible to retrieve the temporaryOfflineCause set previously using a Computer's getOfflineCause method which is the only method available to retrieve OfflineCauses.
Solution
Currently temporaryOfflineCause is a private attribute of the Node class and has been since it was added 11 years ago.
The attribute could either be made public or a getter could be added.
Since the attribute should most likely not be messed with directly from outside - since setTemporarilyOffline should be used for that - I would propose introducing a simple getter.
[JENKINS-67964] Access to temporarily offline cause is impossible
Tim Ploss
added a comment - @mawinter69, thanks for your extremely fast reply.
Yes that PR fixes this issue. Yet at the same time it changes a lot more than is necessary to improve the situation described above.
Additionally PR-6152 makes a lot of changes that could be rejected. I will open a minimalist PR for fixing only the issue described here.
Tim Ploss
added a comment - @ mawinter69 , thanks for your extremely fast reply.
Yes that PR fixes this issue. Yet at the same time it changes a lot more than is necessary to improve the situation described above.
Additionally PR-6152 makes a lot of changes that could be rejected. I will open a minimalist PR for fixing only the issue described here. Tim Ploss
added a comment - More minimalist PR: https://github.com/jenkinsci/jenkins/pull/6337 
This is addressed by https://github.com/jenkinsci/jenkins/pull/6152