Anyone can reset the prepared shares countdown for any other user

[ethereumdegen]

because it is possible to deposit on behalf of other users, anybody can reset each other's coundtowns by depositing small amounts on their behalf, DoSing withdrawals. Most of the protocols that include withdrawal queues force users to make two transactions: the withdrawal request and the actual withdrawal, which would make it optimal in this situation as you want to allow deposits on behalf of other users

[ethereumdegen]

could just ONLY reset countdown if msgsender == lender ?

no -- this wont work

[ethereumdegen]

see branch fix/issue-60 #63