All the content in my panel pages disappeared after this upgrade

Take a look to your pane or region styles... Did you have Panels Accordion or something like that?

I have a similar problem, not sure what the problem is. For me it only affects mini panels put into panels, though,

I am having problems with this upgrade. I get a fatal error on my main page (and nothing else) related to views bonus module which I use to display a view with top, left and right columns.
Fatal error: Call to undefined function panels_print_layout() in drup_root\sites\all\modules\views_bonus\panels\views_bonus_panels.module on line 20

It works again when I revert back to 6.3.3.

After upgrading to Panels 3.4/CTools 1.4 I have had the same problem with several mini-panels we've created (rather than panel pages). I experimented with re-saving or changing panel layouts from two-column to single-column but could not find a convenient way to restore them.

the only workaround seems to be to recreate the panel from scratch.

I tried both views_bonus 6.x-1.0 and views_bonus latest dev version. Same problem

Question: would it be advisable to put back function panels_print_layout($id, $content) {... in files- panels.module (line 881) and display-render.inc (line 55) to get this to work?

At first glance, this seems to get it working again for my case. I see in the release notes for this version one of the changes made:
Removed panels_print_layout() and related functions, as that rendering
approach was old and crusty.

I suppose there was a good reason to remove this, but by doing so, it doesn't work with views_bonus panels. Not sure what ultimately is the best solution. But it would be nice to work out issues with this release - it being a security release and all.

On our site, tabbed panels disappeared after upgrading to Panels 6.3.4 and Ctools 6.1.4. Non-tabbed panels were not affected.

FIXED after patching the Tabs Panel Style module using the patch in comment #15 on #784538: Tabs lost after upgrade to latest ctools.

I think my problem in #2 comes from views_accordion #804526: Doesn't seem to be working with panels-6.x-3.4

This is also happening for me. It appears somewhat random as to what it effects. Both custom blocks, mini-panels and blocks provided by modules are disappearing. Others display the <none> tag where it was entered as the block title (but not all). Also it is impossible to save any changes to a panel - the ajax loading icon just keeps turning after clicking the finish button. I'm not using views accordion or views bonus modules.

This worked fine on the staging site, but not when we pushed it live. In the mean time we had to roll it back. The only difference between staging and live is that staging uses panels from code, whereas the live site has most of the panel pages overridden (though all are affected). I'm not sure this has any bearing on it, I think it's just random.

sub+ nightmare update for me. still not fixed.

I also noticed that various panes have the "None" issue described in #9. I am trying to make out a pattern here but until now I failed. Most of the issues here seem to be related to the ajax/js mess the upgrade brought to us but with this issue I am not sure.

I upgraded panels and ctools to their newer versions (6.x-3.5 and 6.x-1.6) and now it's all working. No panel content disappeared this time and no more problems with the ajax loading in the admin UI. The <none> tags did appear everywhere where I had embedded a block which had the title set to <none> so I had to override the title for each of those and set it to an empty string.

I can confirm that upgrading to Panels 6.x-3.5 and Chaos Tools 6.x-1.6 solves the problem with disapeared panel content.

I'm marking this as fixed. It anyone is still having the same problems with the very latest releases, feel free to reopen.

Not sure if this is related, but I'm having a similar problem with whole panes disappearing. This problem started occurring for me with Drupal 6.17 / Panels 3.5 / CTools 1.6.

There are no PHP errors but I noticed that the troublesome pane is somehow being rendered outside the Panel region during the initial load of the Panels content editor (using single column layout). When I drag it back into the region and save it works fine. Screenshot attached:

I confirm that after upgrade from Ctools 1.3 and Panels 3.3 to Ctools 1.6 and Panels 3.5 all content showed up through panels disappered (Drupal 6.17).
However when i trying to preview pages on Panels admin page its work and show all content correctly.
I tried to backroll to previous versions of Ctools, Panels but this dont work.

I ran into this earlier and discovered that the theme registry had somehow gotten built incorrectly and some layout themes weren't there in the main theme, but worked fine in the admin theme (making it tricky to understand what was going on). A cache clear and a forced theme registry rebuild fixed it.

Thanks, that was so simple!
I flushed all caches and all content visible again! Including APK-type profile pages and standart panel pages.
fixed now

I emptied my cache and still have panels missing. If I open up the panels and resave them with some new content/views then I can see the content. I can't possibly rebuild all the panels I have. I have tried reverting to prior module versions, but the content is still not visible. Thanks when you can!

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Big time upgrade failure for me too. I upgraded from Chaos Tools 6.x-1.3 to 6.x-1.7, Panels 6.x-3.3 -> Panels 6.x-3.7.
First round of updates, I installed Chaos Tools. Symptoms: "less than" none "greater than" appearing in block titles where I've entered "none" in, Panels admin pages totally borked (HTML/CSS showing instead of Javascript tools). I then tried updating Panels to 3.7 with no change. After that, I tried downgrading back and lost all my CSS entries on Panes and was forced to restore the entire database.

How is one supposed to upgrade these two modules? Just upgrading Chaos Tools trashed the site and upgrading Panels didn't fix it.

Edit: Upon a second try, I was able to upgrade with only the "none" problem still showing through. I update both Ctools and Panels simultaneously. I think possibly my problem before came from moving the modules folder (modules had been incorrectly installed in root modules, so I was moving to sites/all/modules). 95% of the modules didn't have problems but I guess Ctools did.

I have narrowed it down to the culprit module - I have Panels 3.2, but upgrading beyond that (3.4 or 3.7) I have tried and gotten the WSOD. Something did go wrong after we moved to another hosting company; all the minipanels and layouts are gone still.