Obviously no webserver is running.
I've done some research, but I can't think of what could have happened. When your system told the 3.20 firmware was invalid, it should have been rejected. But your NSU reports 3.20.
The problem is, the firmware consists of a kernel, an initramfs, and a rootfs, in two mtd (flash) partitions, and a disk partition. These three parts can be written separately, but should be from the same firmware version.
I *think* somehow one of the parts is of a different firmware versions than the others. So this one should be replaced by the right one. The point is, which part is different, and which firmware version are the other parts. As far as I understand you, there are two version of 4.40 and one version of 3.20 possible.
So I need some dates. Can you give the outputs of
ls -la /
That should tell something about the age of the kernel and the initramfs.
The rootfs is harder, as I suppose it's not even mounted. But maybe it is. Can you give
ls -la /ram_bin/
I suppose you are using an FFP stick, right?