Since I started at this company in February there have been three very similar announcements in the manager bulletin board (we can't respond to it, only management can type in it).
'To let you know, X has left the company with immediate effect. Please respect us and X and do not question this any further or contact them about it' (paraphrased but something like that).
One of the people had only started a couple of weeks before.
I don't think it is that they'd all left due to their own unfortunate circumstances either, because this has also happened and the bulletins are much more kindly worded.
Is three people in a year leaving with immediate effect something to be concerned about?