Node keeps losing time

We have a fairly new H500.  OneFS 8.2.2.0.  There are 4 nodes.

One of them keeps losing time - when the time difference gets to be a few minutes I get an alert.  The node that loses time is not a chimer node (the other 3 are)

I go to the web UI, and make a change to time there, and that brings Node4's time to synchronised state.

I'm not sure my approach is the correct one, as this error/alert has occurred more than once now.  What I do addresses the problem, but not the cause. 

Besides changing time in the web UI, is there something I can do directly on the node itself?  Anything to check?