User has to force refresh to clear browser cache [#1650838]

I am getting an issue where users are seeing "old" versions of pages (Boost cache has expired). However, when they force refresh on their browser, they then see the unexpired page (still cached, but not expired).

I thought it was maybe one of these issues:

#829416: anon user can force browser refresh and clear the static cache?
#305071: user logout, Header unset ETag & browser caching front page
#243115: Hosting Issue - Missing mod_headers: logged out user sees auth pages stored in browser cache if previously authenticated

But, unless I missed something, none of those solutions seemed to help.

My .htaccess in the root directory has this code:

  ### BOOST START ###
  AddDefaultCharset utf-8
  FileETag MTime Size
  <FilesMatch "(\.html|\.html\.gz|\.json|\.json\.gz)$">
    <IfModule mod_headers.c>

My host does have mod_headers enabled. I also tried adding FileETag None to the bottom of my .htaccess file (one of the threads suggested that).

None of that seemed to work. Is there a setting within Boost that I should double-check or a change in my .htaccess file? Thanks!