What took me a while to realise is that the two parts in your example are no exact duplicates. The first instance has Dj Vivid 2025 remix and the second instance has Dj Vivid Santana 2025 remix.
If both parts would be exact duplicates, you could use a back-reference like ^(.+?)(?:\s*-\s*\1)$
and replace this with $1
That's because your guessing pattern does not exactly match the real values:
There is no space and minus character in front of %mixartist%, but parentheses around it.
And the field BPM should only contain a number, not 123 bpm
If you were to use a guessing pattern like this: %artist% - %title% ( %mixartist% ) %bpm% bpm - %dummy%
it could work.
As @Florian already wrote above, this only works, if the TITLEs of your friends tracks always contain the "nnn bpm -" part before the second "duplicated" part starts.