Vungle ads sometimes not caching

Hello,

       I’ve integrated Vungle video ads in my Corona Game it was working perfect but few days ago it stopped caching video ads completely, but after few days it stared it self without changing any thing in code. Now it again stopped caching video ads. 

       I suspect this issue is either from Corona or Vungle side but am not sure.

          

local vungleInterstitial = "540e9681c7ec2b6d4400000e"  local videoCompletedCallback=nil videoAddListener=function( event )          if (event.isError ) then         --Cached video ad not available for display         print("problem to show ad")     elseif event.type == "cachedAdAvailable" then         print("cachedAdAvailable")     elseif tostring(event.type) == "adView" then print("called when add is viewed")     elseif  event.type == "adStart" then         print("Corona ads started")         audio.pause()     elseif event.type == "adEnd" then         print("Corona ads ended")         videoCompletedCallback()         audio.resume()     end end showVideoAd = function(callbackFunc)     print("showVideoAd function called")     videoCompletedCallback=callbackFunc;     if ( vads.isAdAvailable() ) then         print(" if ( vads.isAdAvailable() ) then, is true")         print("vads.show")         vads.show( "interstitial", { isBackButtonEnabled = false } )     else local alert = native.showAlert( "Video Ad", "The Video Ad is not available at the moment. Please Try after some time.", { "OK" } )     end end vads.init("vungle",vungleInterstitial,videoAddListener)

Any help will be appreciated.