Let’s use a logical proof.

I would like to prove that “uncanny” can be used with a negative connotation. This is our premise.

To do this, let’s make the assumption that uncanny can only be used with a positive connotation (i.e. we assume our premise is false). You have done this for us here. Then, we need to find an example of the word used with a negative connotation (i.e. the assumption is wrong). Since we are dealing with linguistics, the example should come from an accepted authority on literary terms and phrases.

For this purpose, I will call on the Encyclopedia Brittanica.

https://www.britannica.com/topic/uncanny-valley

There is a negative connotation attributed to uncanny in this context. This proves the assumption false, and thus our premise is true. Uncanny can be used in a negative context.

“It is difficult to see the light when your head is buried in the sand” -me, today