The "I/O error writing PNG file!" (see attachment) happens on a pilot Jenkins instance with only a single job, which runs few times a day. It's an instance with very low activity.
The issue happened twice in the recent weeks (Dec 06, 2017 2:14:47 PM and Dec 20, 2017 5:40:02 PM). It is also to notice that no build was running when the issue was detected (in fact, not a single build was executed on 20.12).
I couldn't find a pattern that points me to any scheduled automated activities from the Jenkins Master itself, except that both happened on a Wednesday...
This ticket has been raised against the BFA plugin because it happened while creating a png related to it. But since it was not directly trigger by a build that runs the BFA, I can't say whether this could have been triggered by the Master itself in order the serve the plugin.
Also, it cannot be detected in the Jenkins interface. Besides the Master's log giving me an exception, I can't find any other anomaly.