Flat form table size object issue

Hello team,
We're building a frontend project using React + Flexmonster, some cases need to store the column widh to somewhere and load it next time, it works fine in Pivot View.
 
However, it did not work in Flat Form, when change the column width of flat form and save the whole report object to somewhere(Elastic Search in this case), then reload this report, found that the Table Size Object as below:
 
"tableSizes" : {
"columns" : [ {
"tuple" : [ ],
"measure" : {
"uniqueName" : ""
},
"width" : 285
} ]
},
 
BTW the Flat Form is in JSON format.
 
"tuple" entry returns an empty array, if there is unique name in it, the column width may works well.
 
How to save column width then reload the target report after saved it? Is this a know issue or something wrong I've made?
 
Thanks.