Transformer-based solution
At the time of the competition, BERT and some other Transformer models were already available and a few solutions with high scores were provided. Here, we will not attempt to replicate them but we will just point out the most accessible implementations.
In Reference 20, Qishen Ha combines a few solutions, including BERT-Small V2, BERT-Large V2, XLNet, and GPT-2 (fine-tuned models using competition data included as datasets) to obtain a 0.94656 private leaderboard score (late submission), which would put you in the top 10 (both gold medal and prize area for this competition).
A solution with only the BERT-Small model (see Reference 21) will yield a private leaderboard score of 0.94295. Using the BERT-Large model (see Reference 22) will result in a private leaderboard score of 0.94388. Both these solutions will be in the silver medal zone (around places 130 and 80, respectively, in the private leaderboard, as late submissions).