Link to 18.06.1 WRT1900AC system image point to WRT1900ACS system image on wiki
Username: Thorkild Gregersen
Origin: https://bugs.openwrt.org/index.php?do=details&task_id=1954
Under the section:
https://openwrt.org/toh/linksys/wrt_ac_series#firmware_images
Devices → WRT1900AC → V1 → Systemimage the link point at
but should be
The SHA is correct when looking at
https://downloads.openwrt.org/releases/18.06.1/targets/mvebu/cortexa9/