half a year ago I had this problem: RUT955 firmware update via cli fails with "sh: out of range" and "Image check failed" - Crowd Support Forum | Teltonika Networks
and now it happened again:
root@Teltonika-RUT955:~# hexdump -C /dev/mtdblock1
00000000 ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff |................|
*
00000070 30 30 30 30 ff ff ff ff ff ff ff ff ff ff ff ff |0000............|
00000080 ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff |................|
*
00010000
root@Teltonika-RUT955:~#