Forcing settings with ethtool and disabling auto-negotiation. 
SSH into CE and use the following command:

ethtool -s eth0 speed 1000 duplex full autoneg off
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Generate file sysctl.conf in /storage/.config/sysctl.d/ with the following lines:

net.ipv4.tcp_sack=1
net.ipv4.tcp_mtu_probing=1

This change is boot persistent (and might revert some hardening).