Thanks for the Details
I can not reproduce this situation on my test install
Since this seems to persist with even minimal settings, we have to try the last possibility, namely to re-isntall the Toolset Plugins manually to avoid possibility of corrupted files.
You mention, this has been working gin past.
Can you locate the Plugin or Theme Update that was causing this issue?
Do you recall, which Plugin or Theme you updated, straight before this issue happened?
In order to avoid the corrupted files, which sometimes is cause of issues, please follow as outlined:
★ INSTRUCTIONS:
?? Backup your website and database ??
• Deactivate/Delete the "Installer" plugin (if you have it)
• Deactivate all Toolset plugins
• Login via FTP to your wp-content/plugins folder
• Delete all Toolset Plugins folders
• Go to https://toolset.com/account/downloads/ and download the latest stable Types Plugin, then extract it.
• Upload the plugin via FTP to the wp-content/plugins folder.
⌥ alternatively you could upload the .zip file using Dashboard > Plugins > New > Upload
• Register the Plugins for your site
⌥ you can do that under Dashboard > Types > Installer
• Download all other needed Plugins
• Activate them in Dashboard > Plugins
This should not generate any problems.
⌥ In case you want to register Toolset Plugins for your site manually please make sure to enter the naked URL of your site in wp-types.com (something like hidden link)
⌥ In the extreme case, please try to register with all non-Toolset Plugins deactivated,
and Theme Toolset Bootstrap enabled.
If this does not help, we will need to reverse plugin version by plugin version, to locate the trouble issuing Plugin / Version.
Since you are working on alive site, I reckoned and offer to send me a site's snapshot, so I can do this for you locally.
If you prefer you can use MAMP or WAMP (local servers) or stage sites in order to do this.
The goal would be to revert to the last working version of your site, an then carefully update each Plugin / Theme one after the other, version by version, until we locate the trouble issuer.
In order to send me a snapshot, we recommend the free Plugin "Duplicator" for this porpoise.
If you already know how Duplicator works
(http://wordpress.org/plugins/duplicator/),
please skip the following steps and just send me the installer file and the zipped package you downloaded.
★ Duplicator Instructions
hidden link
Send me both files (you probably want to use DropBox, Google Drive, or similar services, as the snapshot file will be quite big)
?? IMPORTANT ??
Remember to create or keep an admin account for me before creating the snapshot, or I won't be able to login. You may delete the new admin account once the snapshot has been built.
I will enable your next answer as private so you can provide me the information securely.
Thank you