We're facing a problem when serializing the entire container of nested items. The error is: "Uncaught RangeError: Maximum call stack size exceeded" We were investigating it when all of the sudden we noticed that the very same error is reproducible in the Demo of your own :-) https://gridstackjs.com/demo/nested.html When clicking the 'save' button, the error is exactly the same, visible below.  Great MIT licensed library you've got! We're incorporating it into GRIDNET OS (https://gridnet.org)