As I wrote above, there is really solid proposal to fix this issue: https://gist.github.com/callebtc/ed5228d1d8cbaade0104db5d1cf63939

Actually, there is a really solid and feasible to implement proposal, coming from Cashu author, about monitoring the activity of mints with decent tradeoffs: https://gist.github.com/callebtc/ed5228d1d8cbaade0104db5d1cf63939