Which house?

Fur Planet. I don't know of any other furry-themed publishers as alternatives.

You could try Fenris Publishing, they’re really new and looking for material.

Ouch, but rejection is the norm for the majority of artists. I’ve resigned myself to the fact that I may never sell a print and just do what I want anyway.

It's super common for them to not give a reason why they have rejected a piece (I have only been given a reason twice in my entire 10+ years of experience in submitting to various houses) and it is by no means a reflection upon your skill. Publishers are a business, and sometimes they will reject work that they actually even LIKE solely because they don't think it will be easily marketable. I know it's hard and far more easily said than done, but try not to let it get you down.

There are three other furry publishers out there you could potentially try:
- Thurston Howl/Bound Tales
- Fenris Publishing
- Rabbit Valley Comics

Admittedly, I only have expertise in prose, but I know at least two of these accepts comic submissions. Additionally, I still stand by the notion that I think your Power Penguin novel was great, and even though you self-published it, I know some of these publishing houses are fine with publishing novels that have been self-pubbed before, so if you wanted to publish prose under a publishing house instead, it might be worth it to submit the manuscript to a few of them.