My dnn site just stops responding every few months and all I have to do is to recycle the application pool to bring it back.

Need some help to find out the cause of the issue and any possible ways to fix this issue.

Suspecting that it could be caching problem.

Below is the message from Event log,

StackTrace:

Message:

System.NullReferenceException: Object reference not set to an instance of an object.    at DotNetNuke.Entities.Tabs.TabCollection.AddToLocalizedTabs(TabInfo tab)    at DotNetNuke.Entities.Tabs.TabCollection.AddRange(IEnumerable`1 tabs)    at DotNetNuke.Entities.Tabs.TabController.<>c__DisplayClass34.<GetTabsByPortal>b__33(CacheItemArgs c)    at DotNetNuke.Common.Utilities.DataCache.GetCachedDataFromRuntimeCache(CacheItemArgs cacheItemArgs, CacheItemExpiredCallback cacheItemExpired)