To confirm, are you hosting the Background Update resources locally, or downloading from Adobe servers?
What Flash Player type (ActiveX Control, NPAPI, PPAPI) do you have installed?
SilentAutoUpdateEnable=0 disables Background Updates. If you want to perform a Background Update you need to have AutoUpdateDisable=0 and SilentAutoUpdateEnable=1 in the mms.cfg file
Do you have SilentAutoUpdateVerboseLogging=1 in the mms.cfg file? If not, please add it.
Launch regedit and locate the HKEY_LOCAL_MACHINE\SOFTWARE\Wow6432Node\Macromedia\FlashPlayerSAU registry entry and click on it. Delete LastUpdateCheck entry and run the background Update service again.
Did Flash Player update?
It is the ActiveX Version but may include NPAPI at a later date.
Turns out it was the LastUpdateCheck entry causing this issue! By deleting that RegKey, it was able to work on the external line. But on my corporate Network it still didn't update. I now see these entries in the FlashInstall.log file:
2017-5-17+19-35-15.581 [info] 1631 /pub/flashplayer/update/current/sau/currentmajor.xml
2017-5-17+19-35-36.594 [warning] 1470 12002
2017-5-17+19-35-36.596 [warning] 1474 183
2017-5-17+19-35-36.597 [warning] 1475
2017-5-17+19-35-36.598 [info] 1432
My guess is these may be speaking to the proxy or firewall?
Can you access https://fpdownload.macromedia.com/pub/flashplayer/update/current/sau/currentmajor.xml from within your network?
How is your proxy and firewall configured? If you prefer you can send this information via Private Message. To send a PM, click on my user_name link and then on the 'Message' button link. For reference, include a link to this discussion topic.