I have a similar problem, but I am not using a proxy. PDFs do not download from PMC anymore. I don't even get an error alert - it's as if Zotero is not even trying to download the file. It is working on most other journal sites I have tried, but very slowly.
I have the same problem. I can download the pdf from another sites but not from pubmed central. Before, with zotero 4.x, i could download the pdf from those sites
It is working on most other journal sites I have tried, but very slowly.
Here are two examples:
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5992676/
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5891078/
https://www.zotero.org/support/debug_output
This is the number for the report from the connector: D1711592262.