Nodes not displaying in version 1.26

I was working on a shader just yesterday, and everything was fine. Today I reopen the shader to continue working on it, and the editor doesn't display any nodes. I haven't updated SF or anything, and I was using the exact same version, Unity version, computer I was using yesterday.

I can't add new nodes either. Also, I just tried to open it in another computer and I get the same problem (the other computer is also using version 1.26).

How can I recover the nodes? Remaking it is not an option because it's not a simple shader.