In your approval process,When you have field update actions. There'sedit a tiny checkbox there that says "Re-evaluate workflow rules" or something like that"field update" action of an Approval Process, the checkbox Re-evaluate Workflow Rules After Field Change
needs to be checked in order to have all workflows to be run and evaluated again after the "field update" rules in the approval process are applied.
Check that box...thatThis will cause also causes Process Builder rulesthe flows set in the process builder to be evaluatedrun again.
Please refer to the Salesforce docs to find additional information.