Just to let you know, a lot of uploads are being missed at the moment, most likely MDWS side.
I cannot see any sign of problems over past 24 hours here in the logs or with anyone else except for those few that suffer the same problem for whatever reason. The uploads you are (still) missing just aren't making it to the server.
I suggest you stop DSLstats (unload it, don't just stop sampling), then restart and see if it is okay. It can also happen with DSLstats after a machine has slept/hibernated as I found out here once. Past that I have no idea.
There is a reference upload you can look at (Centurian) that runs from here 24/7 - it has no connection to MDWS and is with a different ISP on ADSL2+ so it's just like any other uploader. If there are server or network problems that account will show it (the U/S SNRM is terrible on it but it works and I just don't worry about it). The only time is will miss is when I update the machine software or otherwise stop it running. It's on 5.8 also.
I only use it as a backup and to software bond with the FTTC line to get another 9+mbps or so d/l and 1mbps u/l, it'll be upgraded to another FTTC line soon.