Infill failure when printing larger prints
I have seen this a lot with people I have helped out in the past. sally infill  or the lack of and weakness in the print is due to an extrusion issue. it looks like you are under extruding. this is why you do not see this in smaller prints. In the larger print you are giving the print head enough time to screw up. You need to look at the tension of the filament on the extruder to make sure it isn't skipping. You also need to do a estep calibration on the extruder. I usually extrude 100mm of filament and measure it to see if it is short. if it is short then it is under extruding and doing a larger print and printing a larger area will reveal short comings in extruder infill.