TL-WR740N v.6 reboot issue

Hello all,
I have a problem with TL-WR740N v.6. I've installed Openwrt and LEDE on a couple of them, but have a problem with "reboot" command . On all of them it is not working, neither "halt".
The last one is with Openwrt 18.06.8 r7989-82fbd85747 / LuCI openwrt-18.06 branch (git-20.029.49294-41e2258) . I noticed also, after power off, the router looses LED setting!
Any help is appreciated !
Thanks in advance!