Missing heartbeats and executors being killed by YARN is nearly always due to OOMs. You should inspect the logs on the individual executors (look for the text “running beyond physical memory”). If you have many executors and find it cumbersome to inspect all of the logs manually, I recommend monitoring your job in the Spark UI while it runs. As soon as a task fails, it will report the cause in the UI, so it’s easy to see. Note that some tasks will report failure due to missing executors that have already been killed, so make sure you look at causes for each of the individual failing tasks.
Note also that most OOM problems can be solved quickly by simply repartitioning your data at appropriate places in your code (again look at the Spark UI for hints as to where there might be a need for a call to repartition). Otherwise, you might want to scale up your machines to accommodate the need for memory.