Openwrt 18.06.3 disappeared from releases

Just yesterday, I changed my router for my company.
I found openwrt 18.06.3,
so I downloaded it. Now the router has become our company's main route and is in use.

But now the problem arises.
I'm going to install zerotier for it, but I found that opkg update returned an error.
When I checked the erroneous urls, I found that they returned 404.
So I browsed again.
I found 18.06.3 disappeared.
I tried to use the 18.06.2 software repository, but the installation prompted the kernel signature error.
Then I plan to use SDK to compile ipk.
But I found that I didn't download the corresponding version of SDK at all.

What should I do now?

A post was merged into an existing topic: Where is 18.06.3?