First of all YES THIS IS BACK.
it looks like the linework suddendly changes after the third panel, it's less rougher like you said. Honestly in the first three panels the linework is thicc enough to make the subjects look good.
In the fourth panel it is less wide, but that's a good trick actually. The more far the subjects are, the more the lines are thin. Linework also depends on the materials.
Not all of it should be the same, it sometimes needs to vary.
Check this drawing for example:
You can see that the lines' thickness varies here. This trick makes more clear the motion, the distinctness and the materiality of the waves.