We've been working away fixing causes of 'unable to decrypt' bugs, to the extent that (as a poweruser) I almost never see them. If you see them, please report them via bug report so we can dig into them.

Meanwhile, the performance of the matrix.org server has definitely improved massively over the last few weeks. We hit a performance ceiling from May through mid July, but since July 19th or so we've finally got CPU headroom back again thanks to stuff like https://twitter.com/matrixdotorg/status/1019957885026144257 and https://twitter.com/matrixdotorg/status/1022095383978233856.