This answer to What “missing satellite” was part of the story of CNN's debut? quotes the 1981 UPI Article The RCA Satcom III-R commercial communications satellite, designed to... as follows:
The original Satcom III satellite was launched successfully in early December, 1979, but it disappeared after a spacecraft motor was fired three days later in an attempt to place it in a stationary orbit 22,300 miles above the equator.
Despite sophisticated tracking systems, the satellite was never located and its fate remains unknown.
and links to the New York Times article RCA Loses Contact with New Satellite which says:
RCA publicity materials said the boxlike satellite was about five feet by four feet by four feet and weighed about a ton.
It's hard to understand how such a large metal object could remain lost forever "Despite sophisticated tracking systems..." Assuming there were at least large pieces of it intact it should still be visible both in satellite tracking cameras if not by space junk-tracking radar. Even in GEO satellites can be seen by amateur telescopes.
Question: How could this satellite be actually lost forever? Are there at least semi-authoritative theories? Or perhaps was it found again much later? (these are 40 year old articles)