Hey Dean,
yet I did not have a look at your g-code because the most usual source of errors like this, especially suddenly after a longer successful use of the machine, is a cable/connector problem, e.g. like here.
If the current was interrupted at the Z stepper, an upcut bit would drill its way down.
To try to track it down, you should re-run the program with ‘milling air’, i.e. without a bit in the router, and check if the Z behaves correctly or if you can reproduce the error.
PS: I assume you clamped the bit firmly with the two wrenches (not the red button and one wrench)
Welcome to the forum!