Recent instances of "Kubernetes API: context deadline exceeded" have been due to a failure to form an etcd quorum (https://etcd-0.***:2379 is unhealthy: failed to connect) which has in turn been due to the control-plane nodes failing a boot-time pivot. I'm not sure if these issues have had Bugzillas filed (if they have, I'm not turning up the bug IDs now). But reassigning to the RHCOS team so they can take a look.
Verified on 4.0.0-0.nightly-2019-04-02-081046
Since the problem described in this bug report should be
resolved in a recent advisory, it has been closed with a
resolution of ERRATA.
For information on the advisory, and where to find the updated
files, follow the link below.
If the solution does not work for you, open a new bug report.