It’s a Lemmy thing not an app thing. I just had this issue. So if Hide Read Posts is enabled, it also hides your own posts, because they are all “read” by you. You just have to disable that setting to see your posts.
But I have this toggle only in app. Not in the lemmy itself. As I understand it is, that the application marks the requests to return only unread posts. But maybe I just understand it wrong.
I’m not sure how the app and website interact, but in my experience, I turned on hide read posts and my own posts were no longer visible until I disabled that. In the actual Lemmy settings it’s phrased opposite, “Show Read Posts” must be enabled, otherwise your own posts become no longer visible.
So I guess, however you changed that, try changing it back and reloading the app, and see if your posts become visible. Are they visible if you log into Lemmy on a browser? 
You were right, it is phrased differently and I had it unchecked. I checked it, and all works as I would except. Thanks!