This isn’t a terrible idea, but it’s also important to understand single-user and tiny invite-only instances as analogous to “leechers” in the torrenting world. The federation load that an instance instance imposed on other instances depends much more on the number of communities it subscribes to than the number of active users. If a user stops using Lemmy but leaves their instance up, it’s generating federation load for no reason.
Tiny instances are inefficient, and while it is desirable for the network to be able to scale to the point where it can reasonably support lots of them anyway, right now federation queues are backed up and messages are frequently getting dropped. Encouraging lots MORE tiny instances is probably not the efficient thing right this second. Rather, we’d want more users joining mid-sized instances that are not overloaded locally and that are making efficient use of the federation load they generate by using it to serve 100-1000 users rather than 1 or 2.
If I had to guess, I’d say lemmy.ml is overloaded and to try again. I think I uploaded an image a few days ago via Jerboa but I’ve been testing different clients and it’s possible I used Liftoff which is another popular android client you could try to see if it behaves differently.
Also, this is the wrong sub for support questions. See rule 2 in the sidebar.