Photos sent to me through Messages never complete downloading

As of a week ago, photos texted to me through Messages on my macbook pro never finish downloading. Instead, Messages remains stuck while showing the grey pinwheel, as can be seen in the attached photo where somebody sent me multiple photos. This error is now happening with all senders who send photos to me. Perhaps 1 in 5 times, the photos successfully download. 4 in 5 times, I see this error.

I'm running the same macOS, with the same security, same iCloud, on the same wi-fi networks (I've tried 5 different wi-fi networks), etc. as I have always run. Nothing has changed on my end. This is not solved by logging out of iCloud and back in, nor is it solved by rebooting.

[Edited by Moderator]