Was the newly named stick insect Anchiale robusta already known to scientists?

Yes. The University of Sydney says the insect now named Anchiale robusta had long been known to scientists and enthusiasts but had been misidentified for decades.

Researchers combined DNA analysis, museum material, field surveys, citizen science records and captive populations to reassess its identity. ABC News also reported the recognition of A. robusta and interviewed the lead researcher about identifying distinct species.

Here, new species refers to scientific recognition of a distinct species, not the first time anyone encountered the animal. The accessible sources document the announcement and reporting; the underlying journal article was not accessible during this check.