Note 5
When you change your FOV in your settings, when you move your player's head, it changes the position of the fishing line.
Linked issues
is duplicated by 8
relates to 2
Comments 7
Duplicate of MCPE-10591 or possibly related? (Though in that bug, the line is not connected to the float when looking around)
Confirmed, because the fishing line is one of the GUI, it proved when you enable the experimental options "Hide GUI" .