<p>Testing my new Wanhao i3+. PLA plastic(Wanhao), basic normal quality settings in Cura (I guess 0.1 mm layer, 40 mm/s speed, 60c bed temp, 200c extruder temp). After 1.5 hours of printing quality degraded, it makes some loose structure. </p>

<p>Edit:
After finish I noticed that problem exists only in layers where it cycles printing/no printing. There is no problem on layers where it print continuously.</p>

<p>What is the reason can be and how can I fix that?</p>

<p><a href="https://i.stack.imgur.com/W90dj.jpg" rel="noreferrer"><img src="https://i.stack.imgur.com/W90dj.jpg" alt="enter image description here"></a></p>

It definitely looks like under extrusion.
First thing I would check is the filament feeder to make sure it has
a good grip in the filament.
After that I would do another print to see if the problem is repeatable.
If it doesn't repeat, it may have been
A temporarily clogged nozzle
The filament was undersized in that segment and the filament feeder lost its grip.
The extruder got to cold for some reason in that segment and the feeder couldn't push the material through the extruder fast enough.
If it does repeat:
Re-inspect the filament feeder
Try increasing the the extruder temp to say, 225.
Try turning off retraction to see if it is related to those settings.