I would PID tune the hotend temperature. It doesn’t look like a mechanical fault like a stepper motor issue or belt.

If you look at each layer, the striping is offset every layer somewhat consistantly and it looks like something is turning on and off on a regular interval, with the same pattern of “blips” in between. (The stripe seems to happen every x mm of printed line.)

Plastics will behave and look different depending on what temperature they are printed at. There are typically glossy and matte sections in every print, actually. You may be hitting a temperature range at one of those texture-transiton points. A few degrees high, it may be translucent. A few degrees low, completely opaque. If that range is within your existing PID tune, that might contribute to the visuals here.

Even with your micrometer, you are only measuring the widest layer over x layers. If your temperature is not stable, it could also contribute to some lines being thinner and more translucent.

Testing extrusion rate by weight is a method that might be good here. Print 100mm of filament into a blob and weigh it. Change the temp a hair, print another blob and weigh that. Create a chart of 10-20 tests to see if there is a spot where extrusion is inconsistent. In your case, we want to replicate that striping, but for a weight test instead. The weight of the blob will change if hotend temperature is affecting extrusion rate. You need a good scale and preferably one that can weigh into hundredths of a gram. That precision is not required, but it helps.

The reason I suggested a weight test is because your temps might be swinging between a temperature that is good and also just a hair too low.

The hotend “heating response” might be laggy, is my guess, regardless of what may be causing it.

Edit: The hotend temperature is kept constant in “bursts” of power. There might be a threshold where the hotend power is just full-on.

Represented in a series of H’s and L’s (H for high, L for low), here is a pseudo-representation of what I see each layer and it matches a heating pattern of hotend but with a lower limit where its “full-on” heating:

HHHHHHHHLLLLHHLLLLHHLLLLHHHHHHHHH…

It’s not a perfect pattern in your case because a dozen different things contribute to final nozzle temperature.

No.