My bank did not withdraw the funds for a check I wrote

First, make sure you've got something in writing that your landlord has received rent. Second, put something in writing to the bank seeking an explanation why your account was not debited the amount in question. Third, wait for written acknowledgement from your bank before letting your balance dip below the amount in question. Fourth, if unsatisfied by anything above, consider a bank upgrade.

What happened? Probably an error by the bank. Or maybe a kind of race condition as tenant deposited funds to the account to cover the check while the landlord was presenting the check to the bank. I've had a check from a tenant go through then get called back for non-sufficient funds and then I had to rerun the check.