If you want to trigger the registration of DOIs manually, then you have a problem if this is to be done for very many contributions at the same time. There is no option to “Mark all”!? Does the user really have to click countless checkboxes individually? The problem seems to exist in the Crossref plugin as well as in the DataCite plugin. I suggest to create a possibility to mark all contributions (or to place the option better, if existing).
Several times, I tried to register, or update plenty of doi records at once. I almost always get a Gateway Timeout Error when I exceed 20-25 submissions by using Crossref plugin.
But, I could register about 400 records at once by using XML export-import method. I checked 100 articles using the Crossref plugin, exported them, and joined later in a single xml file. Then uploaded to Crossref. I remember that I had to check and correct some XML nodes.
Crossref also provides a metadata quality check before uploading the XML file to the live system.
Nevetheless, I would also like to get “select all” button on such functions too.
There is work being done now to improve bulk registration of DOIs for Crossref. That won’t be available in 3.3 but it’s actively being worked on so we hope it will be available soon.