First off, I see two g-code commands in your file that are not in the Marlin g-code reference: M84, M400. What post processor are you using? The current recommended post processor for Fusion 360 is Don Gamble’s update to the Guffy post processor. See this topic for what a link.
But since you are getting this error in the middle of the file, not at the beginning or the end, I don’t think these g-code commands are at the root of your problem. My two shot-in-the-dark theories are that 1) the post processor is outputting non-printing characters, or 2) there is noise on the line you are using to send the g-code.
After looking at your GCode I would recommend reviewing the following post processor parameters:
Scale Feedrate = false
First G1 → G0 Rapid = false
G1s → G0 Rapids = false
Allow Rapid Z = false
Changing these will not correct the noise issue but will address possible other issues.
By not scaling your feedrate your z changes may be exceeding the MPCNC’s max z.
The hobby version of F360 produces no Rapid moves. While this would seem to be only speed related, it is not. Each cutting should start with a G0 rapid. A rapid moves first in Z then in XY. Without it a drag can occur getting to the start of a cut.
The last two parameters will simply speed up the overall cut times.