hi richard,
the document id is scheduled to been assigned daily on sharepoint online.
given the situation, i suggest you wait another day and check the outcome.
if the issue persists, please confirm the following information:
- have you ever used the feature normally?
- when did you enable and configure the document id settings?
- provide the screenshots of your document id settings and the id for a document.
to upload a screenshot, click use rich formatting just under the textbox, then select this icon
and browse to choose files.
regards,
jiaxing bian