You are using Release process, you create an ASN and the Due qty is reduced. When you create the GR for ASN, the due qty is reopened.
This can be caused by 2 things.
The DELSHED_in or the RDN_in xml contains creation and change timestamps in local time, this is not mapped to UTC in SNC and creates a mixup in the changetimestamp of the Release. You need to send these timestamps in UTC and there should be no issue. For sending these in UTC, you can implement note 858447 on ERP side.
The other issue is wrongly configured due qty calculation. The correct setup is the following.
In SPRO navigate to the following node:
Here you set the Relevant ASNs parameter to Selection Based on Time Stamps.
If you send the xml-s with UTC timestamps and have the customizing set up like this, the due qty reopening issue should not occur.