Wheel cylinder keeps popping out?

Image never loaded, so here it is.

Thanks for the image. I would replace the rear brake shoes and drums; this happens because they are out of spec.

Here are the shoes for $49.00:

https://amzn.to/3KP7cfs

And the drums for $59.00:

https://amzn.to/45A3aj5

Here is a generic guide to help you step by step with instructions in the diagrams below to show you how on your car:

https://www.2carpros.com/articles/how-to-replace-rear-brake-shoes-and-drums

Check out the images (below). Please let us know if you need anything else to get the problem fixed.

Thank you for replying, but that's a bigger problem because those are new brakes, I put on a month ago and everything I did matches the guide.

You may have the incorrect wheel cylinder installed? If the shoes and drums are new this is the only thing I can think of.