Hi,
The release strategy re-triggering depends on the release indicator used and it will re-trigger only if there is a value change or new strategy is determined. If you are simply flagging acknowledgement in a PO, it wont make any value change / new strategy and hence new release wont be triggered. Please check the note: 493900 - FAQ: Release Strategy Question number 3
Also, please check whether version management is activated for the PO document type. If version management is activated for the document type and acknowledgement indicator is marked as version relevant field, then the new version will be triggered once the acknowledgment field is changed, which eventually may trigger release strategy again. Refer the note: 1961482 - Reset release strategy when version number is set as Characteristic in Customizing If this is the case, please check whether the acknowledgement field is version relevant or not. If its maintained, it may re-trigger the release, if all the release configuration is maintained correctly.
Regards,
AKPT