There are several threads which refer to the way the ST automation engine triggers routines. One of these is here
https://community.smartthings.com/t/automation-help-timed-automation-doesn-t-seem-to-be-triggering
and you might find it interesting to scroll through.
Several users, myself included, use a rule to run a check switch every so often, while designating the conditions, ie your humidity levels, as preconditions.