Relationship between pets

@wl2lst55ny Do you have Mods or CC? If you do, please try moving your Mods folder to your desktop and delete the localthumbnailcache.package file, plus delete any other folder in the "The Sims 4” folder with the word 'cache' in the title. (When you restart the game it will automatically create a new Mods folder.) 

You can also try a game repair and make sure your game is up to date.

Are both animals healthy and in good moods? I assume you're seeing the female with the hearts animation (indicating she's in heat). Do you have at least one 'open slot' in the household size to make it possible for them to have/add one or more puppies (pet and sim pregnancies cannot occur if the household limit is already full).

There's also this Bug Report that may be of interest to you on the 'Be Nice' interaction not working on dogs:
https://answers.ea.com/t5/Bug-Reports/OPEN-CD-Be-nice-to-interaction-not-working-on-dogs/m-p/6594049#M57280

Please update us on how it goes. Thanks!

SheriGR ☕ – I don’t work for EA

Hi @SheriGR 🥳 I get this in my game as well with no mods or CC. One of my Sims has two cats and they just don't get along very well. One of them even has the Friendly trait and neither of them are Territorial or Mischievous. Both are generally happy & well-cared for (to the point of being spoiled!) and neither of them run away from home. They've been in the same household for a long time now (I have aging disabled) so whatever relationships form between two pets should be well-established between these two by now. All I can think of is there must be some kind of hidden quirks and traits for pets influencing this behavior. Like a "cats are jerks" trait! xD

https://www.ea.com/games/the-sims/the-sims-4/news/cats-dogs-personalities

@wl2lst55ny I've been looking for some way to fix this through cheats but I have not found anything yet. I have a similar problem with one of my saves (see above), but I'm not currently playing that save. The next time I play I was planning on trying to change some of their traits through testingcheats + cas.fulleditmode to give them both the Friendly trait to see if that has any effect. If either of your dogs have the Aggressive trait, you should probably try changing that first.

I know it's not the same as having puppies the old-fashioned way, but your other option would be to open your household in Manage Households, click on one of your pets, and then select Add a Sim + Play with Genetics to add as many puppies (with both of your dogs as the parents) as you want, as long as you have enough room in your household (8 Sims max).