Heat Tape Marks After Pressing Glass Photo Block

[Bri1]

Hi could anybody please give me some advice on what might be wrong with Heat Tape Marks Being Left after pressing .
I have been pressing Glass Photo Blocks

vB_ID:4968

20171221_180327.jpg (86.93 KiB) Viewed 6 times

vB_ID:4968

20171221_180327.jpg (86.93 KiB) Viewed 6 times

at 200 degrees Celsius for seven minuets as instructed, but after pressing I have noticed that the tape marks are appearing on the blank after the paper has been removed .
I have shown an example of what I mean in the pictures .
I wondered if it might have anything to do with the heat tape needing replacing as it is quite old, or failing that lowering the temperature on the press?
I just wondered if anybody has experienced the same thing and have some advice as to what I might be doing wrong