After restoring database: Panels panes display as empty

I recently moved my Drupal databases to a dedicated MySQL server; after restoring the databases, all Panels panes display as empty. However, the Panels layout is still visible (screenshot attached), and the panes' content is still available when editing the panes. Even the Panels built-in preview displays as empty. Clearing all caches (something like drush cc [all] or through admin_menu), or re-saving the Panels did not bring the content display back.

This applies sytematically to roughly 20 Drupal 6.30 sites (actually, it's Pressflow); all Panels are affected, including the home pages and landing pages. Views embedded in the panels run normally when run separately. All other site content appears to be available and accessible, as in the old installation. This appears to be an isolated Panels issue that does not affect any other parts of the Drupal sites.

I have migrated Drupal sites with Panels before and never encountered anything remotely similar.

Checks made so far:

• ./admin/reports/status does not report any issues; especially Panels claims to "operate normally" and the "CTools CSS Cache" says: "available";
• Apache's error logs do not show anything related to Panels, especially no "PHP fatal error";
• Pressflow has been updated to the latest version available on Github (equivalent to Drupal 6.30);
• All contributed modules have been updated to the latest versions;
• Caching appears to run smoothly; I'm using Memcached and APC; no new caching layers have been introduced so far, especially no reverse proxy (like Varnish) is involved;
• Drupal's Watchdog log is an issue for itself; the amount it logs depends heavily on the setting "error_reporting" in php.ini and ranges from "nothing" to "totally unreadable". My current setting is error_reporting = E_ERROR & E_RECOVERABLE_ERROR & E_WARNING which reports nothing related to Panels or Ctools (Debian's default is error_reporting = E_ALL & ~E_DEPRECATED & ~E_STRICT, which makes the log unusable since any Drupal module appears to emit some annoyances)
• Most of the Panels pages are really simple (used for layout stuff) and do not include conditions that might check for a hosts IP address; I don't think that these Panels pages should even notice that they have been moved.

The existing Panel pages can be edited normally; new content can be added to the panes, but does not display in preview, like the old content. The same applies to newly created Panels pages: they can be created as before, but display no content, neither in preview nor when accessing their URL.

Versions:

panels   6.x-3.10     2012-Jan-18  Supported, Recommended, Security, Installed
ctools    6.x-1.11     2014-Feb-12  Supported, Recommended, Security, Installed

The Panel pages code is rendered like this in the browser; this fragment of the complete page has not been alted or reformatted:

…
<div class="panel-region-separator"></div><div class=" prosper-lightgraybackground-border" 7>
  <div class="inner">
    
    
    
    <div class="pane-content content">
          </div>

    
      </div>
</div>
<div class="panel-region-separator"></div><div class=" prosper-lightgraybackground-border" 8>
  <div class="inner">
    
    
    
    <div class="pane-content content">
          </div>

    
      </div>
</div>
<div class="panel-region-separator"></div><div class=" prosper-lightgraybackground-border" 9>
  <div class="inner">
    
    
    
    <div class="pane-content content">
          </div>

    
      </div>
</div>
…

I have no working Panels page for comparison, but the generated code looks broken (numbers at the end of closing tags?)

I'm pretty much out of ideas; any suggestions?

Thanks!