Check the required setup
Start with the hard requirements before assuming the route is broken. The Breeding Farm needs a valid male and female parent assignment, Cake needs to be available, and the base layout needs to let the assigned Pals stay near the farm long enough to work.
Separate setup issues from route issues
A correct route can still feel broken if the farm is starved of Cake or the parents are not staying assigned. A wrong route is different: the pair may breed, but it will not produce the target child you expected. Troubleshoot those two problems separately.
Use a short test before a long session
Before committing rare parents or a full passive project, run a small test with a route you trust. If that works, the farm loop is probably fine and the next check is the specific parent pair or Cake throughput.