This has occurred with other flowmeters and sounds similar to this issue in 2023: https://mhra-gov.filecamp.com/s/d/JC2zcBITk2olCpwX

In 2024, the standard ISO 15002 was revised and now includes a requirement to test specifically for this problem. The requirement is the flow should not change by more than +/-10% in one hour after a flow rate has been set. The rationale for the requirement explains orifices made of viscoelastic materials (e.g. polymers) can continue to deform for some time after a load is removed (e.g. when the needle of a valve is moved from a closed to an open position).