This problem was reported by partner. The trouble is that for various reasons the context path may be missing which results in invalid SQL like path selector in get_child_contexts() - we need to verify the path is valid before using it. The problem is that the get_child_contexts() may be used when deleting data which resulted in deletion of all contexts in several existing sites when using some add-ons...

Short term solution:

1. print debugging message when get_child_contexts() on contexts that do not have path or depth and return empty array
2. prevent deleting of system context

Long term solution (new issue to be created):

• prevent deleting of invalid contexts in UI
• add CLI tool for diagnostics and rebuilding of context paths
• add more debugging notices to inform admins that there is something wrong with contexts
• add more debugging info for admins that try to insert data directly to database tables without rebuilding the contexts
• maybe add workaround code for invalid contexts that tries to lookup children using some other info