corrupted downloaded files - help needed to pin down source of problem

[AD1242]

I've been having issues downloading ubuntu images, the file i get is always corrupted (md5sum of downloaded file does not match original one).
i've replaced cables and have tested a lot of different combinations to try and pin point the source of the issue:

1. on my mac: wget ftp://ftp.cuhk.edu.hk/pub/Linux/ubuntu-releases/cosmic/ubuntu-18.10-desktop-amd64.iso -> corrupted file. different md5sum every time i download the file.
2. on my NAS: wget ftp://ftp.cuhk.edu.hk/pub/Linux/ubuntu-releases/cosmic/ubuntu-18.10-desktop-amd64.iso -> corrupted file. different md5sum every time i download the file.
3. on my laptop, same wget -> file is ok, md5sums match. i've tried multiple times

at this point i thought the problem lied with the powerline connection between my mac and my router but:

4. copy file from my laptop to the mac, or from my laptop to the NAS -> no problem. i've tried a few different ways of copying the file (using netcat, using http etc.) it always works fine.
5. i've also tried copying the file from the mac to the nas and vice versa, this also works fine.​

what am i missing? what could be the source of the data corruption?

i attach a diagram of my network setup for clarity. all lines are cat5e or above cables.
i've tested / replaced them all with new ones, the results above didn't change.

thanks in advance for your help!

 

[degrub]

likely the difference is the software/protocol used to manage the download.
Try a different download protocol.

 

[AD1242]

i tried http over the internet, same issue: the mac or the nas will always download corrupted file.
however between my laptop and my nas or between my laptop and the mac, no problem (i served the files over http on my laptop using python3 -m http.server)

 

[degrub]

Have you tried connecting the Mac or NAS directly to the Linksys lan port ?

 

[AD1242]

not yet, they are in different locations at the moment (hence the PLC adapters) and moving them is rather inconvenient (need to turn them off etc.)
if no other diagnostics ideas, i'll try this in a couple of days

 

[sfx2000]

not yet, they are in different locations at the moment (hence the PLC adapters) and moving them is rather inconvenient (need to turn them off etc.)

I suspect it's the PLC's...

try the download directly over WiFi provided by the router..

 

[AD1242]

@sfx2000 : i thought it might be, but in that case why aren't downloads corrupted when i serve them from my laptop rather than from the internet?

@degrub : i haven't had yet time to try to connect the nas or the mac directly to the linksys router via ethernet, but will report back as soon as i do

thanks both for your help! i hope to be able to figure it out as it is driving me insane!