Well first of all I strongly recommend staying at 24% or less infill. PLA is amazingly strong. I'm not sure that 40% is any stronger than 24%. Usually 24% is enough. Cura used to change the infill pattern when you went above 25%. I'm not sure that it still does but the pattern changed to where it onlyl did diagonal lines in one direction and then the next layer was the other direction. This ended up being heavily underextruded because layers would be printed in the air every time.
So I would change that first.
The next thing I would change is to make the infill speeds the same as the outer shell speeds. Which printer is this? um2? um3? other? Cura 2.X tends to make the infill speeds too fast and you get weak, underextruded infill. Also when it switches from a slow print speed (low head pressure) to a high infill speed (high pressure) it takes a little while to build the pressure back up and meanwhile you get underextrusion.
That could be why you get underextrusion in only the start of an infill section.
If those 2 things don't help I would just slow it down. Print the top layers at half the speed you are printing now.
I would also do tests. I would create a cad version of the above model that only takes 15 minutes to print - just print one small section - maybe 2cm by 2cm and only maybe 1cm tall (for a good test you want to get at least 1cm above the hot glass to mimic the cooler temperatures found farther from the glass surface - and maybe also lower bed temp by 10C just for this test).
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gr5 2,172
It's better to post the images right in your post so people don't have to do extra clicking. I feel especially sorry for people who browse with their phones. Also other people may have the same issue and I'm wondering if you will keep your photos on devestechnet as long as ultimaker will host the photos.
I think this image sums it up best
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