An update to the WordPress SubHeading plugin was committed on Wednesday 2nd December, which added the ability to completely remove all stored subheadings when deactivating the plugin.
This new ‘tidy’ feature was enabled by default, but I failed to remember that during the plugin upgrade process the plugin was deactivated and then activated once the new version had been successfully installed.
Because of this and the ‘tidy’ setting active, the hooks I had in place always (wrongly) assumed that it was a new install, rather than an upgrade, and therefore may have removed all the subheading values you had set.
As of version 1.2 this feature is disabled by default, and checks for any previous version of the plugin before resetting your options and deleting the meta values (subheadings).
Apologies to anyone who has suffered from a loss of data, and I hope all these issues are now resolved as of the latest version (1.2).