php 7 framework builder issues / debugging

I have a little problem which I can hope someone can help me with.

I have a site which uses framework builder quite extensively, and I am attempting to update and upgrade it so it is compatible with php 7.

I am slowly working through the problems, such as getting rid of mysql connections and updating deprecated files such as the ecart definition.

I now have many pages working ok, but some will simply give me an error like this…

Fatal error: Allowed memory size of 134217728 bytes exhausted (tried to allocate 32768 bytes) in C:\xampp\vhosts\xxxx.php on line 1

Weird thing is, if I comment out the line which includes the ‘plugin’ page, the ‘parent’ page loads ok
If I just load the plugin page, that also loads ok.
If I then take the code from the plugin page head and body and paste it into the ‘parent’, this also works,

The problem may not be the same across all pages, but I am just trying to find a procedural method to debug this.

Any help appreciated