The warning message means that the Executor is unable to send the Heartbeat to the driver (might be network issue). This is just a warning message, but each failure increments heartbeat failure count and when we hit the maximum failures the executor will fail and exit with error.
There are two configurations that we can tune to avoid this issue.
Interval between each executor's heartbeats to the driver. Heartbeats let the driver know that the executor is still alive and update it with metrics for in-progress tasks. spark.executor.heartbeatInterval should be significantly less than spark.network.timeout