14 January 2014 Microsoft announced that they will disable code-base sandbox solutions in SharePoint Online. And in this blog they say “We realize that our customers have made investments in coded sandboxed solutions and we will phase them out responsibly”. But just suddenly they communicate via Office 365 message center this “In approximately 30 days, currently running, code-based sandbox solutions in the SharePoint Online environment will be disabled.” Haven’t seen this announcement jet (4 august 2016) in our tenant but others have.
If you don’t know if you have this solutions, try this PowerShell script to analyze what kind of sandbox solutions exist in your SharePoint Online. The script is posted from the Office Dev PnP group.