Logged out by homepage

[Aramaech]

We've been having an ongoing issue for about the last month and a half:

1 ~ When you visit the home page, you appear to be logged out.  Clicking on any other page from there will bring you to the page, logged in.
2 ~ If you check your cookies, you're still technically logged in on the homepage, even though it appears you're logged out.
3 ~ This bug pops up seemingly at random, but once it emerges it remains active until some temporary fix makes it go away.
4 ~ The temporary fix that worked in the past was rebuilding the search index.  This would subdue it for about a week, give or take.
5 ~ My initial assessment was that it was an indexing problem, because the search index table was also damaged due to a bot that forced us to reset, losing 2 weeks worth of data, which is when the problem started.
6 ~ Having fixed every single thing in the database, and converted all tables to InnoDB format (faster, self repairing), I thought the bug was gone, but it's emerged again today.
7 ~ Rebuilding the search index no longer fixes it.
8 ~ Our host believes it's a server side caching issue, however we've had them for over 10 years and never had this problem.
9 ~ Our other admin thinks it has something to do with the themes or IPS's caching system, because if you change the theme on the home page and reload it, it goes back to the original theme.
10 ~ When the bug is active, reloading the home page is instantaneous, suggesting no backend processing, but just html processing.

Does anyone have any idea what could possibly be causing this or how to fix it?  
We're both relatively tech savvy, the other admin more so than me, so please feel free to include any details that might be helpful.
Any help would be very much appreciated.  Thanks!

[seanzol]

I believe this is just the end user's browser caching the homepage from before they logged in; a hard refresh (Cmd-Shift-R, or Ctrl-Shift-F5 iirc) should get things back to normal

[Fast Lane!]

I get this error too.  Homepage visit shows logged out but forums they are logged in.  Seems to pop up on mobile phones a lot.

[mark007]

Here, too