Hello Michel michelcheret
Thanks for reaching out.
Our team has been looking into the issue and trying to replicate it locally, and it seems that it works properly on our side.
The status "Completed" in Inventory Log removes it from appearing in Stock Central but doesn’t change the stock quantity.
So, please, note that to reduce or increase the stock from the Inventory Log, you need to select the product and click on the product row. Then it will change the color to pink and the change buttons will be displayed.
Here you can see the tutorial on how to reduce or increase the stock from an Inventory Log.
If you have further questions, please let me know.