problem with update in legacy mode

Hello there, i have this update issue since the last patch 7.2 .. and it's only happen on legacy client i have re-installed LoL a couple of times, and nothing happened .. i keep getting "unspecified error occurred. please check the logs for more information" .. i have also tried HRT with re-patch and re-install .. started it with adminstrator ..and i still get the same thing , is there any chance to get this done without using the new client?

if you're asking why i don't want to use the new client .. that's because it's run so slow in my pc it has had caused me to get lower priority queue .. and whenever i wait the 20m and click "Accept" to start a game .. the client itself doesn't respond at all! so i just go back to wait another 20m.. so can you please find a solution for this and reply to me?

Thanks in advance.