My question is have there been any other missions, or individual crew
members, that have been sent up "again" to complete a task?
STS-75's main payload was a reflight of STS-46's main payload due to the failure of the Tethered Satellite System (TSS) on its first attempt. Sadly, STS-75 failed as well, but in a different way, ending this system's flight attempts, and kicking off a large number of silly UFO theories.
It wasn't an exact mission reflight like 83/94, but several crew members who were trained in operating the TSS flew on both: Nicollier, Chang-Diaz, and Hoffman.
On STS-46 the tether jammed in the deployer after the satellite had only been deployed a short distance. This was traced to "fixes" made to the deployer shortly before launch.
On STS-75 the tether broke after deploying a significant distance.
This was traced to manufacturing errors with the tether.
Another example is Charles Walker who flew on three separate shuttle missions to operate the McDonnell Douglas experiment Electrophoresis Operations in Space.
This wasn't due to a mission or experiment failure though, but was part of the pre-Challenger-failure attempts to commercialize the Shuttle. Walker was the first non-government/commercial astronaut in history.