I have found a further solution to the UE-P3 crash.
Playing on Steam, I tried the delete the P3 folder, and turning off cloud saves but it did not solve the crash for me.
I had only downloaded the demo at that time.
However I recalled that some games WILL NOT launch on the EA App, if I have a VPN running.
I paused my VPN and Immortals of Aveum launched perfectly.
Also I only paused my VPN, so it automatically became active again within minutes as I played Immortals of Aveum. This caused no problem with playing the the game whatsoever, including when closing down the game and Steam syncing.
On the EA App you may need to pause the VPN to launch Immortal of Aveum. Then again when you close Immortals of Aveum. I can only hazzard a guess at that, as I bought mine of Steam.
Problem is 100% solved for me.
I often launch Immortlas of Aveum to continue playing, and forget to pause my VPN. This brings back the UE-P3 crash message.
Again, just pause VPN and the game launches again no problem.
I bought the game the moment it went on sale. Loved the demo and the game is equally as good, if not better. .... A real shame this stand out title has suffered so terribly from review bombing.