Currently Being ModeratedFeb 2, 2013 12:50 PM (in response to GaryKing)
I spent the past few days battling this exact problem and believe I have fixed it.
I believe this actually is an ISP related issue (even if that sounds like BS at first). I do not have these problems when I use the internet at work, or use my personal hotspot on my phone, but I do have them on my home internet (Comcast).
I believe that when iTunes Match begins uploading, it maxes out the uplink bandwidth of the Comcast connection, renders it useless and causes the connection to time out. iTunes Match thinks the connection died, and it stops, then restarts.
The way I fixed it was limiting my maximum upload bandwidth via my router. My router (Netgeard WNDR3700) has a setting that allows me to set up maximum uplink bandwidth. Speedtest.net told me my connection had 4-5mbps up, so I limited it via my router to 2mbps.
As soon as I did this, my uploads began working without timing out and restarting.