I wrote a Fax-Out App for a client that's been in production for quite awhile, working fine. Client sends about 1200 fax-outs per day. In the past two weeks; the client's RC call log shows the Fax-Out Status as "unknown" for one particular number - always. And, sporadically for other numbers. All of the Status - Unknown faxes never reach the recipient. The RC App status is 100% Success, no errors for the App in the Developer Portal. The status returned within the App is "Queued", which is normal. I need to determine if the issue is 1) The App 2) The Client's RC Account 3) The Recipients setup. We have been working on patching CVE's for PCI compliance the past few weeks; but would assume if anything we've done in that regard would have blocked communication with RC Servers and we would see errors on the App Status screen. Any thoughts on how to trouble-shoot this issue?