Postgres special character rendering

I have an old Sql Server db with a ‘free entry’ field that is being accessed via a Postgres 10.6 foreign table. This field contains a lot of garbage characters (higher than Ascii 128) which Postgres has a difficult time rendering and results in ‘empty looking’ records. I say empty *looking* as I am able to query those missing records out of the foreign table using the regexp_replace function to substitute spaces for those problematic characters. This leaves me with two questions: 1) The Postgres database encoding is UTF-8, so shouldn’t that be able to render any characters properly? 2) Since I can query it, the Postgres db is obviously processing this data at some level. Why does it display that entire field as blank until the special characters are replaced?