"ERROR: timestamp out of range" converting epoch stored as bigint to a timestamp
When I paste the value 1527012834506374 into  https://www.epochconverter.com/ I see the warning: 


  Assuming that this timestamp is in microseconds (1/1,000,000 second):


Postgres' to_timestamp() assumes an epoch with seconds, not microseconds, so you need to use:

select to_timestamp(1527012834506374 / 1000000.0)