Landline callback problem



I activated the callback service on UCM6510 and it works perfectly from the mobile phone.
If a mobile number calls the dedicated callback number, UCM calls me back and regularly allows me to contact an external number.
The problem is if the caller calls the number dedicated to the “Callback” from the landline, the answer does not take place correctly, therefore it is not called back.
Ideas on how to solve it? (of course the caller must have the clip visible in order to be called back).

n.b .: UCM6510 today fw -> I have to update it to shortly