Microsoft Edge 44.18362.1.0 and also the same on Internet Explorer 11.175.18362.0
I have only just noticed this. Logging on to MyBT I have the remember me ticked so my correct BT ID is populating the BT ID field. However when I click on Log in I immediately get an error "Please enter your BT ID" above the correctly populated BT ID field and nothing happens.
To log in I have to click on the Not you? Log in and select the same BT ID that was already in the BT ID field!
The only clue that I can offer is I don't have a firstname.lastname@example.org BT ID. It doesn't bother me enough to try clearing my browser cache and history which may get it working correctly.