Welcome to this user forum.
I assume this is a direct fibre connection, and its the ONT which is showing the alarm?
Have you spoken with the FTTP team on 0800 587 4787.
It could be a faulty ONT or a bad fibre connection.
How many times have you reported this fault?
I assume your phone also comes down the fibre link as well.
This is going to be a fibre or ONT fault, it could even be a dirty or loose fibre connection, it will not be your home hub.
They should start by checking the light level with an optical power meter.
If that is within limits then the ONT needs changing.
I am not sure if one of the moderators can chase this up, but I will ask.
Unfortunately they cannot help, so all you can do is to keep complaining to the FTTP team, and ask them to get Openreach to do the checks that I have suggested.
It Openreach that look after the fibre connections.
Just to clarify, there is no reported FTTP problem by Openreach. In fact there is only one affecting 12 customers in the whole of the country in Leytonstone and that is an MBORC one.
Are you dealing with the ordinary helpdesk or using the number of the dedicated FTTP team @Keith_Beddoe has posted above?