BUG #16148: Query on Large table hangs in ETL flows and gives out of memory when run in pgAdmin4

The following bug has been logged on the website:

Bug reference: 16148
Logged by: Scott Volkers
Email address: scottvolkers(at)gmail(dot)com
PostgreSQL version: 9.5.15
Operating system: PostgreSQL 9.5.15 on x86_64-pc-linux-gnu, compiled
Description:

We have a large table and the error occurs with this where clause:
FROM "elliedb"."documentlog" WHERE dcmodifiedutc>(extract(epoch from
TIMESTAMP '2019-11-15 11:30:51')*1000)

When we reduce the scope to current time - 4 hours the query works within 44
seconds.
where dcmodifiedutc > '1575282651000'

Is this expected? Is this a version issue being only 9.5? It seems the
timestamp conversion would be done once and applied to the filter, but it
seems to ballooning the query result being aggregated for the where
clause?
Thank you.