Can you provide some information which database you tried and which query you tried? Maybe also the permalink to the document? The extraction of keywords and tags from EBSCO should usually work.
After i activate the checkbox "Automatically tag items with keywords and subject headings" in my preferences/general, the keywords/tags can be downloaded. Thanks for this hint!
Upgrade Storage
Do keywords/tags work on other sides? Did you check your preferences that the option is activated, see https://www.zotero.org/support/preferences/general ?