Snippet of chat when i discovered this Bug:

[5:47 AM] RawrMaoster: ok i got it to work i just didint give it a priority x-x altho { } i cant use 😢 there goes my cool prefixes
[5:50 AM] RawrMaoster: Maybe you know why when i do [-{Owner}-] it displays as [--] deleting {Owner}
[5:52 AM] Turbotailz: put it in "" ?
[5:55 AM] RawrMaoster: Neither " " and ' ' work
[5:56 AM] Turbotailz: ¯_(ツ)_/¯
[5:56 AM] RawrMaoster: shame
[5:57 AM] RawrMaoster: i had pretty cool prefixes xD

So in summary, only because i dont use [Owner] like other servers i found a bug with how i display my groups when using the .yml configuration.

[-(Owner)-] << Works - Normal Brackets ( ) << Output: [-{Owner}-]
[-{Owner}-] << Breaks - Squiggly Brackets { } << Output: [--]

So the Squiggly Brackets dont display with the text inside. So {Owner} Gets cut from the prefix in the chat on a live server.

groups.yml Example: (Pretty much empty cause im slowly learning luckperms and 2 other plugins slowly)

owner:
  permissions:
  - displayname.[-{Owner}-]
  - nucleus.broadcast.
  prefixes:
  - '&4[-{&5Owner&4}-] &5':
      priority: 10

Seems to be working for me

> lp creategroup owner
[14:47:05 INFO]: [LP] owner was successfully created.
> lp group owner setdisplayname [-{Owner}-]
[14:47:13 INFO]: [LP] Set display name to [-{Owner}-] for group owner in context global.
> lp group owner info
[14:47:44 INFO]: [LP] > Group Info: owner
[14:47:44 INFO]: [LP] - Display Name: [-{Owner}-]
[14:47:44 INFO]: [LP] - Weight: None

groups.yml

owner:
  permissions:
  - displayname.[-{Owner}-]

My guess is that Nucleus is using { } brackets as part of it's chat formatting definition, so this part of the display name is being replaced. I suggest opening an issue there. :)