Flabbergasting issue with ethernet connection

[GloW]

Hello,

I have an issue that i can't make much sense of.

Here was my network setup :

Router -> BPL -> rpi3 : All is working fine

I deciced to use the rj45 in the walls for a better bandwidth, the connection is a bit flimsy, So I frst made sure this was working ok :

Router -> RJ45 wall -> Laptop(ArchLinux) : once I'm able to get a carrier all is working fine
$this->bbcode_second_pass_code('', '
cat /sys/class/net/eth0/carrier
1
...
')

So I put the ethernet cable in the rpi3, expecting it to work, but :
$this->bbcode_second_pass_code('', '
cat /sys/class/net/eth0/carrier
1
sudo ip link set eth0 up
sudo dhcpcd eth0
...
timeout
')

Not knowing what to do next, I plug a switch (actually a wifi router in access point mode) like this

Router -> Wall RJ45 -> switch -> rpi3 : All is working fine !

I just can't make sense of it.
I also tried with static ip, I get routes but nothing is going trough.

[bulletmark]

There was a shocking bug causing problems like this introduced in the kernel package linux-raspberrypi 4.19.37-2 and fixed in the latest 4.19.42-1 so make sure your system is up to date.

[GloW]

$this->bbcode_second_pass_code('', '[pi@alarmpi ~]$ uname -a
Linux alarmpi 4.14.94-1-ARCH #1 SMP Wed Jan 23 02:59:35 UTC 2019 armv7l GNU/Linux')

Looks like I'm fine. Do you have the link to the issue though ?

[bulletmark]

@GloW, the offending commit was added in 4.19.37-2 but was completely reverted in 4.19.42-1 so you certainly don't have *that* bug. The serious issue was https://github.com/raspberrypi/linux/issues/2964.

[GloW]

I've updated my system fully, but this issue is still present. No idea what to do now.