lock transaction should use a high priority feerate 
From what I recall, the lock transaction fee is set as low as possible, which during high fee environments means that it may take too long too confirm. The swap tool times out after 2 hours on mainnet waiting for the lock tx to confirm. 

_Originally posted by @delta1 in https://github.com/comit-network/xmr-btc-swap/discussions/1563#discussioncomment-8590798_