I know this issue has been reported numerous times, but I wanted to give an in-depth breakdown of this glitch. I have done some testing and I have discovered the exact cause.
Upon receiving the Ro Bin egg, the player is able to hatch it in or out of their inventory. This feature is what causes the bug. If the player chooses to hatch the egg in their inventory the following bug occurs: A Ro Bin will hatch from the egg, however the egg will remain in the player’s inventory. This egg will then EVENTUALLY hatch another Ro Bin (It should be noted that if the egg is dropped onto the ground AFTER the Ro Bin has hatched then the egg will disappear). This is just one of the various methods to get multiple Ro Bins. If you set the egg on something like a shelf, overtime the egg will gradually begin to hatch until it eventually reaches a point where it can hatch. As described above, the egg is not consumed when the Ro Bin hatches, because of this, the egg will continue to hatch spawning more and more Ro Bins until the player eventually decides to remove the egg from the shelf and place it on the ground. The last method combines both of the previous methods, keep the egg in your inventory until it hatches into a Ro Bin, then place the now “hatched” egg into Ro Bin (not entirely sure if this is necessary), then into/onto a container such as a shelf, it will start producing Ro Bins almost immediately.
The Rock egg is not being properly “consumed” from the player’s inventory /a inventory causing the glitch to occur.
Obtain a Rock egg, and then use one of the following methods listed in the description.