see https://github.com/ZeroK-RTS/Zero-K-Infrastructure/issues/536

if you participated in a battle with 98.x engine, you already have a local copy of the replay.

if you click "watch replay now" on this page, the downloaded file with something in the name like "98.xxx develop" becomes "98.xxx[colour=red]%20[/color]develop" an got 0 kb size. looks like it cannot overwrite the existing file, creates a new one with a strange name but dont write into this second file.

try loading from local copy (worked for me) or delete local copy and 0kb copy, then try again.

btw. some work as manual download for me, some don't

Okay. my copies are in .config/spring/demos ... but there was an announcement I thing for folder change. But that folder?
Anyways this is solved for my case.
But problem still exists for zeroK page. I will post under the other issue