Function model undefined while opening mapping in PI 7.3 dual stack

Hi Experts,

I have added some duplicate structure in target structure as part of mapping change. It is not multimapping, it is simple mapping and Idoc to XML scenario.

PI version is 7.3 dual stack.Transported changes moved and imported successfully from Dev to Quality.

While opening mapping in Quality system, getting error "function model undefined".

I have seen all blogs related to this error and most blogs telling this will come when target structure chages however in my scenario i just used existing structure as duplicate structure (Right click on target node in mapping --> Duplicate subtree).

Few blogs says, need to apply few patches (SAP_XIESR,SAP_XITOOL,SAP_XIGUI) in PI 7.11, but my system is PI 7.3 dual stack.

Few blogs says, need to re-import, this request i have already submitted and mapping will re-import again tommorw.

Mean while I am just curious to know, why we will get this error? Is there any proper solution to fix this issue?

Thanks for your inputs in advance.