Additionally, only when leveling up a pet using an evolution stone will you now definitely receive a partner.
Zudem erhaltet ihr nun bei der Aufstufung eines Begleiters mithilfe eines Evolutionssteines ganz sicher einen Partner.
First a bit of background on how upgrading pets to partners work-s/ed before patch 103.
There exist two methods of recieving a Partner from 'a pet'/pets.
It is possible to fuse two level 10 pets and recieve a partner (this has a 100% success chance afaik).
It is possible to use an evolution core on a level 10 pet and have a ~10% (?) chance to recieve a partner and ~90% chance to have your pet loose some exp.
It is also possible to fuse two pets which are not level 10 but chances of recieving a partner are not 100%.
Rephrasing the english patch notes would result in:
The only way to definitely recieve a partner when leveling up a pet is by using an evolution core.
Rephrasing (and translating) the german patch notes would result in:
When leveling up a pet by using an evolution core you now always recieve a partner.
The english patch notes appear to imply that fusing two level 10 pets is being nerfed to no longer have 100% success chance.
The german patch notes appear to imply that evolution cores are being buffed to 100% success chance.
Removing the word 'only' from the english patch notes would result in the two forumlations converging to the german one.
Altering the word 'nun' to 'nur' in the german patch notes would result in the two formulations converging to the english one. (Although this would still be ambiguous and allow for evolution cores to be buffed to 100% success chance.)