Hopefully fixed for the next release.
For how the item spawning works for this item (and a couple others): when the item is discovered it is flagged to be positioned at that location and will remain there (for the most part)--for about 2 days for the Strange Egg and Mango. A hidden cooldown timer starts to keep the item in its place and prevents you from discovering another until the timer expires. once that happens, you can have the chance to rediscover the item, even at the same location. If you pick it up, the cooldown timer will decrease to about 20 minutes and the item's position (now fixed) should be reset. This is how it should normally work.
For the Strange Egg, it won't be rediscovered if you already have one in your inventory (so you can store, drop or sell it if you want to find it again). For its Myrellion encounter, it is intentional that you can rediscover it again regardless if you already have one in your inventory. So essentially, if you pick up an egg on Myrellion, after 20 minutes, there is a chance you can find another one while still on Myrellion.