In short: front end (like, page design) dev added a line in code that would call home for a list of people and instances dev didn't like so they won't appear on the front end to users. Badically a unwanted blacklist of users. Many got there for one reason or another. Some have no clue why.

lemmy is federated. this means two people on two different instances can talk to each other as if they were on the same instance.

multiple instances have websites they administer. these admins can install custom user interfaces to make it look/feel different from other instances. one of those custom interfaces is "tesseract".

the lead developer for tesseract had a file obfuscated and hidden that has a list of communities, instances, and more importantly users. this list would hide/remove content from these communities, instances, and users based entirely on the whims of the lead developer. this means if you were reading my comment from one of these instances that uses tesseract, you wouldn't see my comment because I am on the list.

the developer in question is @ptz@dubvee.org you can direct any questions to them about it.

To add to what others are saying, your instance does not support Tesseract anyway, though if you read your instance sidebar text it points to Photon & Alexandrite frontends as options if you wanted to change the way that Lemmy looks to you (and if you use a browser rather than 3rd-party app).