Failed flow filters means that one or more of the configured trigger or profile filters against the flow prevented a profile from entering a flow.
For example, a profile may not enter an add to cart abandonment flow because they have since placed an order.
Or, a profile might not enter a browse abandonment flow because they have since added to cart or started checkout.
If you click into "Fails Flow Filters", you can identify the failed filters.
If you identify any flow filters that look inaccurate, consider removing the flow filter.