infill getting thinner

So I come with a new problem.
Here is the image:

You can notice how the infill is getting thinner as it goes. The perimeters turn out quite well though…

The thing is, I keep the speed pretty low (30-50mm/s),
and the temperature is 230C (abs). So I am thinking, could this be a extrusion width problem or something more sinister, like nozzle clogging etc.?

I’d check that the bearing on the idler wheel turns freely still, the small gear on the extruder motor is locked down and tight at the setscrew, and that the filament itself is able to feed freely without binding or snagging on anything. Could also theoretically be a hot end heater or temperature sensor issue or possibly but extremely unlikely nozzle clogging. There is also a very small possibility your hotend shifted during the print and is offset from the hole in the extruder

edit could also be shavings clogging the hobbed bolt chamber.

It seems that you were right. A little bit of cleaning out the gaps between parts solved it!
Thank you