For the last few weeks I've had trouble downloading from Google Photos files. It only happened on large files; videos & zip files of multiple images. The problem only affected Chrome - the files would download fine using Firefox. For single images the download would work so I decided it must be something related to the files size. A lot of googling and it seemed to only affect me so I removed and fully reinstalled chrome, that didn't fix it.
I found similar problems in the help forum but none of them had solutions (technically, one did by changing the download folder location but that didn't work for me).
I used developer console to see what happened on the page and try and get more of an error message. I found "load resource: net::ERR_QUIC_PROTOCOL_ERROR". I then googled that and found a page on stack overflow suggesting that disabling QUIC would help, and to disable it here: chrome://flags/#enable-quic
What is QUIC? It appears to be a protocol to improve performance of pages of the network using UDP. There were mentions that some networks/routers/devices don't work properly with this format. I don't know which part of the network between me and Google Photos is at fault, but once I disabled QUIC the downloads completed perfectly. If you want to know more, you'll need to research it from here yourself. Sorry, I have work to do :-)