COPY Command spawning multiple processes

I have a lengthy data pipeline that imports a CSV, creates a sequence of dependent views and then exports the results using

as a CSV. This process had been working fine, completing in around 30-60 seconds. Suddenly, this process has started running much slower when it reaches the copy command. Running

usename, state, query FROM pg_stat_activity;

shows three identical, active

commands under my username. The process does eventually complete but now takes up to 20 minutes or more. Other than changing some initial sub-setting, the data has remained unchanged. No one else is using this database but there are other users on the cluster. Has anyone encountered this behavior before? Does anyone know what might cause a sudden slow down in a

operation? Postgres 11.6, RHEL 7