Gaza and Sinai for one. Not a big deal as there's almost certainly no city there. But also the chunk out of South-eastern Egypt is a bit conspicuous unless there's historic reason for it. I've definitely missed a city there once or twice on flip because of that gap.
SE Egypt I can actually understand. The exclusion was part of the then Axumite empire that resisted the initial Arab onslaught. Having that area flip would be clearly ahistorical. Two of the three tiles are tagged "Massawa" for the Ethiopian player, which is a city in modern Eritrea that was part of the Axumite Empire. Massawa only fell to the Arabs in the 8th Century. Same for the remaining tile, tagged "Adulis".
I too am puzzled by Gaza and Sinai. Caesarea held out for a year but it's too far north and anyway, a year is nothing. Gaza and Sinai were on the main invasion route into Egypt and all of Egypt was gone by 642 (barring the brief recapture of Alexandia several years later - which is my justification for - where Aelxandria doesn't already exist - founding Xou, which is outside the flipzone, and calling it Alexandreia

).
Leoreth, if you are going to review the Arabian flipzone then I strongly disagree with the incluson of
Crete in it. Flipping Crete is completely ahistorical.
Cyprus was
raided from 649 but only later (c. 688) became jointly administered, and
Crete did not fall until the 9th Century. I can kind of understand it strategically (it removes a useful naval bridgehead from the human player, the AI is seriously bad at seaborn invasians, and it pretty much guarantees war with Greece, if Greece is alive, because Crete is in the Greek core) but it's still a bad idea.
However, as mentioned, my main puzzlement is over the Ar-Rutbar tile, which has very little impact on game play, yet someone cared enough about it to explicitly add it to the Arabian flipzone exclusions list.
In my current Byzantine play-through, when I originally capured Babylon it had only 1 population point and I was actually tempted to raze it and found Ctesiphon on the excluded square

; but that would destroy the Great Sphinx and would also cramp Carchemish and Tyre, so I let Babylon survive. I did cheekily found Tanis, in Sinai, to stop the Arabs from reinforcing Egypt before I could get there. Carchemish and Tyre make better bases for the recapture of the Levant and Mesopotamia than Babylon anyway. Carchemish retains most of its hinterland and is just two infantry moves from Babylon, and Tyre is a 100% legitimate beachead that allows me to instantly recapture the undefended Al-Kuds from the Arabs using the two Cataphracts I received when Persia declared war on me at my own spawn. Galleys out of Athens let me instantly drop an Archer in to retake Knossos (ironically, the very Archer pulled out of Knossos two moves earlier), and I could have continued with three shipborne units to invade Egypt if necessary. It's not necessary in my current game as I have both Xou (renamed to Alexandreia) and Mut and I recaptured Al-Uqsar out of those instead. By 636 AD I have recaptured and regarrisoned every city that flipped to Arabia. Meanwhile Harun al-Rashid has lost two Camel Archers in a scuffle SE of al-Kuds, is locked into the Arabian peninsula, and is begging for terms. I am considering whether I should offer peace now, or if I should invade Arabia and bleed him of units to make the peace last longer.
(Note that even extending the Arabian flipzone to cover all of broader Egypt and Sinai would still only delay the Egyptian reconquest by the number of moves required to bring a Cataphract down into Egypt after recapturing al-Kuds, or else for a Horse Archer landed on the Mediterranean coast to move inland. It would not help newly spawned Arabia at all.)
Checking in WB, I found an Arabian Legion in Sana'a. I was going to grumble over having an irreplaceable Legion flip to the Arabians, but then I couldn't identify where I had lost it from. So I reloaded my 331 AD save and checked:
Turns out he wasn't one of mine. I bet that guy has a story to tell!