Repeated instance ID

Hello everyone,

We just finished a survey including different partners in different regions with a total number of surveyed household of nearly 3000. We are experiencing now the following weird issue:

For one single partner in one specific region, there are 70/515 observations with the same instance ID but 3 different ID devices, some questions with the same answers but not all the questions neither.
We didn’t define the instanceID, using the default one. It is very particular to have that situation for one specific partner. and only one.
Anyone have any idea how such a phenomenon can occur, have experienced it or have an idea on how to replicate it?

Thank you very much for your halp and insight about this issue.