Sounds like it's switched accounts
@LOAM :
https://www.amazon.co.uk/gp/help/customer/display.html?nodeId=201628040
Get your dad to say "Alexa, switch accounts" and see what happens.
He done that tonight and it's confirmed it's using his profile.
To clarify
I have an Amazon prime subscription and my dad has been a "household" member for several years as they benefit from free delivery.
We have two echo's which are both registered to me, which we have had for about a month. My dad has one echo which is registered to him which he's had for about a year.
Until this week the only devices I could see on my Amazon Alexa app were my two devices.
I don't really understand this bit but my dad says that around Wednesday he became aware that his device was giving out the weather report for the city that we live in, not his location. When he checked, the device was showing as being located at my address but still registered to him and he says he corrected this and nothing more
Yesterday our devices were giving weather from my dad's location, when I checked they were set to his address.
I can now see (and edit) my devices and his, and he can see (and edit) his and mine. My two devices are listed as being registered to me, my dad's device is listed as being registered to him.
My dad is receiving dispatch/delivery notifications for our orders as well as us.
If I send an announcement from the app on my phone it is played on all 3 devices one if which is 120 miles away and not registered to me.
I can edit my dad's echo from my Alexa app, including changing and seeing which wifi he is connected to.
My dad doesn't have a prime account, he is part of my accounts "household" so it's not possible for him to have added me to anything.
I'm struggling to understand how announcements are being played on a device that is not registered to me, in a different user account.