In patch 9.8 you cannot play back replays recorded in earlier patches. It doesn't matter whether these are you own replays or someone else's. I suspect this is related to only being able to install an SD client in 9.8 - I guess the 9.8 SD client interprets all 9.7 and earlier replays as being HD and therefore cannot support them?
Hopefully you are working on a fix for the lack of HD client support? I see it is widely reported on Wargaming's forums as well as this one.