> * Hmmm... good question, anyway I can determine that post upgrade? I've upgraded to 1.29 of copy artifact and then almost immediately to 1.30 since it appeared then so I don't have "downgrade to X.YY" shown with the original version that I've started
> * had issues with some other plugin and one led to another
> ** unfortunately I went the wrong path
As there are cases you cannot downgrading plugins easily (e.g. the configuration fields are changed), you would better determine you need a new version BEFORE upgrading.
Anyway, this problem seems caused by Jenkins core as Daniel points, you should switch your Jenkins core to the LTS versions. It might also resolve problems with other plugins.
> maybe copy artifact plugin could be extended with some retry procedure in case of file copy issues?
That feature could not help you as the slave crashes and the build cannot continue anymore.
JobRequeue-Plugin might help you. (As I haven't tried that plugin, I recommend you test that plugin before introducing to the production environment.)
> seems that slave node is dying (not 100% sure if related and what happens first - slave down or copy problem), here's the entry from log file
This log file is the one stored in the master, isn't it?
(8mha:AAAAWB+LCAAAAAAAAP9b85aBtbiIQSmjNKU4P08vOT... is an annotation appended by Jenkins)
Please check the log files in slave nodes. They are placed in JENKINS_HOME you specified in node configuration pages.