I suspect it is a bug in subgrid. Three cases described the exactly same behavior after enabled “expandOnLoad: true” in subGridOptions. Basically only half of the subgrids expended, and the rest of the rows can't be expanded even by clicking the triangle manually. More descriptions can be found at the link,

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I checked with firebug, it looked like the html/javascript got messed up starting from the second half of the grid rows.

I use jqgrid version 4.1.2 with xml data, and another user said he use 4.3.1 with json.