What About the Neighbors?
Okay, if the ancient Egyptians are going to have medieval technology, what about the neighbors? Social and technological changes do not occur in a vacuum. If one power develops, say, a 14th century level of tech, then the others will have something close to, if not better than, that.
Of course, what neighbors we're thinking of depends on the historical period. New Kingdom Egypt had very different neighbors than Old Kingdom or even pre-Dynastic Egypt. Heck, Egypt herself went through a lot of changes in the 3,000 or so years between the unification of Upper and Lower Egypt and the start of the Christian Era.
And how does the tech develop in the first place. All advances depend upon previous advances. You cannot smelt iron until you can make a fire hot enough.
Casting iron take a fire even hotter.
Which ties into the specific ancient Egyptian historical period. Early Old Kingdom Egypt was a neolithic society. Copper tools was the best they could do, bronze would come later, and through trade with her Asian neighbors. While it is possible for a neolithic society to develop iron smelting, it's not easily done. (A source of iron ore also helps.) So the earlier you want the Egyptians to have medieval tech, the harder it's going to be to justify it.
One possible solution is to have it introduced by an outside agency. In the realm of alternate history a favorite is the precipitous introduction of parties from the future. In S. M. Stirling's
Island in the Sea of Time it's very late 20th century Americans on the island of Nantucket and the U. S. Coast Guard training ship, Eagle. In Eric Flint's
Shards universe (
1632, 1633, etc.) a mining town is transported back in time and space to Central Germany in (that's right

)1632.
Or, you could use the ever popular Alien Space Bats (ASBs). A critter first 'invoked' by the crew at [soc.history.what-if] to "explain" alternate histories so implausible only outside intervention could justify them. While originally intended to be derogatory, some have started using ASBs in a more serious manner. Eric Flint for example, with his shards of extraterrestrial origin mucking with folks and locales.
So now you have more things to think about.