Sweet32: Can a single 8 byte block session ID be exploited by this vulnerability?
What I understand from the sweet32 papers, ciphers relying on a single block without any CBC or something will be safe right?


Yes Sweet32 applies to ciphers with block sizes of 64 bits in CBC mode. The idea is to collect enough ciphertext to find a collision (which due to the birthday problem will be around $2^{32}$ blocks), in other word two ciphertext blocks that are equal. 

We can write these blocks as $E_k(C_{i-1} \oplus P_i), E_k(C_{j-1} \oplus P_j)$, as in CBC mode we encrypt the XOR of the plaintext block and the previous ciphertext block. We note that since the blocks are equal it must hold that $C_{i-1} \oplus P_i = C_{j-1} \oplus P_j$. We know what the ciphertext is so if we write the equality as $C_{i-1} \oplus C_{j-1} = P_i \oplus P_j$ we know the lefthand side and recovering the plaintext blocks becomes equivalent to solving a two time pad.

Note that beside only working on 64 bit ciphers in CBC mode, this attack also requires a huge amount of data. I think in the paper the researchers observed hundreds of gigabytes of ciphertext before finding a collision. Given the amount of data needed (I doubt you have hundreds of GBs of session IDs), and the fact that you are not using CBC mode you are not at risk.