Hello @MTP ,
Yes, there are indexing lags after a successful submission. The XML API indexing is quicker than the REST API indexing. The XML API usually takes two hours or so to index newly registered or updated works.
The REST API and search.crossref.org (powered by the REST API) can take up to 24 hours.
You can read more about this here: Ticket of the month - September 2023 - A DOI-namic timeline
Warm regards,
Isaac