After upgrading armbian to 26.2.1 with kernel 6.18.10 performances on WAN interface dropped to 20Mbps for a single TCP connection. The interface is end0, renamed from eth1, driver from ethtool -i is "st_gmac".
I used armbian-config to rollback to kernel 6.12.58 and performances are ok now.
Will it be fixed in the future kernels ?