I did not include him in the list because hipposworld.de said no hippos were present at the zoo as of 2021 and the post you linked to was from 2020.
Halterdetails
Translated from German as best as possible: "The zoo opened in 2015.
In June 2019, the enclosure was still under construction; Hippolit lived in the elephant house. Completion was planned for autumn 2019. The zoo planned to acquire another animal in 2020.
On January 1, 2019, there was one bull elephant at the zoo. Unfortunately, no further information about this animal is available. As of January 1, 2021, there were no animals at the zoo."
Hippolit arrived there from Port St. Pere as a 21-month-old in June 2019 (he was born 9/1/2017), but there hasn't been much if anything stated about him or the zoo having hippos since then, there could be many possibilities, he could have died shortly after arrival, he could still be there today, or has since moved elsewhere. Until there is further confirmation on what happened, I am considering him to be lost-to-follow-up. I hate when that happens, especially in today's time but it unfortunately does happen a lot more frequently than we think, especially in European zoos.