Hi, I wanted to ask a question, and I was wondering if there is a way to fix this problem. So I recently started breeding a pair of Riolu's, and Gastly's. I've been waiting a few hours for them to breed and yet there wasn't any hearts. I even added a Golden hour glass and yet there still wasn't any hearts! I made sure it was the right environment and everything, it even said that they were "Falling madly in love every single day"! If there is a way to fix this bug/glitch please tell me as soon as possible. Thank you! 
Hi Keasim,
I'm sorry to hear you are having issues breeding! Here are some reasons why you may be experiencing this issue:
1)
Touching the breeder before the Pokemon spawn in. If you interact with the breeding machine before the Pokemon spawn in, then the timer will reset, resulting in no colored hearts. Always important to exercise patience!
2)
Breeding Pokemon of the same gender. Evidently, breeding Pokemon of the same gender will not result in any egg, and thus, no hearts!
3)
Breeding Pokemon that are "Baby" Pokemon. From the Pokemon you mentioned above, Riolu is unable to breed as it is classified as a "Baby" Pokemon, which are unable to breed. For a complete list of these Pokemon, click
here.
4)
Visual Glitch. On occasion, there will be a visual bug where no hearts are showing, but the Pokemon will continue to breed. If this happens, you can try relogging, but no worries if the hearts don't show up!
Hopefully, this information helps out to some extent. If you need anything else, please feel free to let us know and we'll help you out as soon as possible! Stay safe and healthy.
Cheers!
