‘Sorry, there was something wrong with the download.’ (Not the language issue)

Hi, I’m getting the error in the title when trying to add this add-on to our Project Server. I saw the language issue on your support page, but the server and the install were both already set to English (United States). I’ve tried redownloading multiple times, as well as with the other language options, without success.

At another level (site content –> your apps) the error is different, saying ‘You can’t add this app here’, with no extra info. And if you view the app within the contents page, the bulk edit app is just grayed out.

Any ideas what could be causing that? Thanks