stat_add_date is wrong for many members in stores

Summary

The newly shown stat_add_date is showing false values for many members of our cooperations. They should show the correct date of adition or some "n.a." value.

Steps to reproduce

Open a store on beta and hover over the members of that cooperation. See the first line beeing wrong.

What is the current bug behavior?

Team members show addition dates of the store creation or some random dates we can't reproduce

What is the expected correct behavior?

The text should show the date of addition into the store. For all members which have been added before this release, it should just show "unbekannt" or alike.

Relevant error messages and/or screenshots

In this image, the stat_add_date has been set to the value of the last fetch.

Possible fixes

get rid of all methods setting this value but the new one which gets triggerd by addition.

Clear the column of the SQL table which holds those wrong values.