bt mail (not Yahoo) contacts missing from groups on ios devices
I created groups on BT web mail and added contacts to the groups successfully.
When looking at mail on my IOS devices (iPhone SE and iPad) I can see and select the groups but only a few of the contacts are then displayed from the group I selected, usually about 2 or 3 out of 10 or more contacts originally added to the group).
If I select all groups then all of my contacts are displayed as expected
The groups works perfectly from BT web mail so it seems there is an issue syncing groups to IOS devices.
Can anybody advise what the problem is and how it could be resolved