Can’t say I know what I’m talking about but there’s been a tonne of organisational changes spread across 4 updates that have just been integrated all at once. This seems to include a revamped notification system and a whole host of organisational changes advertised as improving interactivity and individual site modification by the end user. I’m no expert but it seems likely that facilitating this required modifying the way existing content is logged, links to each other and is filed.
My best guess is that a few of these changes updated the logs and triggered the new notification system (does that make any sense?) while the sheer weight of them caused it to blow up.