Error Downloading files into Zotero
We are working on a systematic review currently, and earlier Zotero was working fine. Now it says there is a translator issue. The owner of our group just purchased the unlimited storage plan, so we shouldn't have issues with the storage. Zotero has made this project very complicated and we have had to restart our project several times now because of Zotero problems.
(nothing to do with storage)
Depending on the database you're using, good chance you're seeing https://www.zotero.org/support/kb/site_access_limits
Hard to say anything about the rest -- people use Zotero for systematic reviews all the time, though.