Outlook IOS on multiple Apple Mobile Devices (Keeps signing out)

Using MS Outlook 365 on 2 Windows computers, and 2 Apple devices (iPhone 7 & iPad Mini 4) with Outlook IOS.

Setup & signed in to icloud,com email account on both devices, but after signing in on second device, the first device shows "Please sign in to your xxxxxx@icloud.com account".

After I do sign in, then the second device shows same message.

Have tried using same & different app specific passwords, with same result.

Two other (non-Apple) email accounts work normally, only the icloud account does this.

Any thoughts group?

Roy