As per title. I'm not even talking about moves that take longer to mate. These forcefully transpose to the solution in the same number of moves.
Case #1:
en.lichess.org/training/37823
Solution starts 1... Qe3+ 2. Kh1 Qe1+
The alternative 1... Qf2+ is falsely marked incorrect even though 2. Kh1 Qe1+ forcefully transposes.
Case #2:
Solution starts 1... Rxh3+ 2. gxh3 Qg3+ 3. Kh1
The alternative 1... Qg3+ 2. Kh1 Rxh3+ 3. gxh3 again forcefully transposes in the same number of moves.
Case #1:
en.lichess.org/training/37823
Solution starts 1... Qe3+ 2. Kh1 Qe1+
The alternative 1... Qf2+ is falsely marked incorrect even though 2. Kh1 Qe1+ forcefully transposes.
Case #2:
Solution starts 1... Rxh3+ 2. gxh3 Qg3+ 3. Kh1
The alternative 1... Qg3+ 2. Kh1 Rxh3+ 3. gxh3 again forcefully transposes in the same number of moves.