2. It can leave one open to niche attacks and one becomes vulnerable to these cyber thieves who will extract private keys from signatures after a transaction has been made.
3. Quantum computers could extract private keys if these addresses are re used.
The attacks only work if the same nonce is re-used over and over again by the wallet [most wallets plugged that vulnerability 8-10 years ago] or if there is some mathematical relationship between the two nonces e.g. K' (the second nonce) being equal to K+1 or something else equivalently simple. So don't expect to find an equation out of a linear congruential (rand(3) family of RNGs) or Mersenne Twister RNG.
All secure wallets generate a random nonce for each transaction, mitigating this vulnerability.