Printing Problem, need some help.

I have a Flashforge Finder 3D printer. Until recently it's been rock solid. Now, it will occasionally print with an odd defect. Certain layers will not be "complete" for lack of a better term. It will complete the print, but there will be horizontal sections that are "thin" and it will break apart along those lines. The image is an example. I'm printing a Star Wars pistol in 3 parts. The lower part came out perfect, this (the middle) part came out as pictured. This will happen for a few prints, then it will print properly. I recently replaced the nozzle thinking it might be the issue, but this print was after the nozzle replacement. Any ideas? Maybe the hot end needs replacing??

could be something as simple as filament that has inconsistent diameter.
It's fairly rare these days as even the cheap stuff tends to be fairly diameter consistent. But what you have is intermittent under extrusion and that's one of the possible causes.

Temperature fluctuations in the hotend would be another.

A slightly dodgy cable causing the stepper motor voltages to fluctuate is another.