I am experiencing the same between 18h00 and 20h00.
On the Xperia im running both Java and the PPC version of Mxit, so if the one doesnt log in, i use the other platform and it logs in first time aroun.
This is strange coz both of them connect via socket, not HTTP. So log in protocol is exactly the same for the 2 versions. Also, a soft reset goes a long way to getting you to log into mxit. It seems asif your device id resets to a newer number after a reboot and then Mxit server gives you right of way over the older device ID?