If the root cause of the problem is the Toppy not coping with the size of the EPG data download, then the explanation of why it only just started is that the amount of data being downloaded increased with the addition of 10HD and 7flix and in regional areas Nine affiliates adding duplicate LCN for Nine, NineHD, which added to the duplicate for 9Go.
If you did a rescan early, there was a place-holder in the IceTV EPG, and EPG data was added slowly. Eventually it got to a critical mass, causing spontaneous reboots.
Delta Mike Charlie has pointed out that the reason why ABC 2 appears to be the culprit is that it has a very large number of very short programs, hence a big hunk of EPG data to be downloaded. Disabling ABC would have the same impact as disabling two or three other LCNs.
It looks like my 5300 may be having problems (it has not done an EPG fetch for a while), hopefully it is not in a reboot loop.
Ian