I notice on the log when a bet's odds are updated the log entry has OK_REMAINING_CANCELLED suffixed. Does that mean that an updated bet is first created at the new odds and then cancelled at the old? Could that mean that in that instant I need enough funds to allow for both of the lays?
Not by Betting Assistant, it happens at Betfair’s end.
I keep excess funds in my Australian wallet when I'm testing stuff in case I make a cock-up. If one bet was being updated at the same instant the offset bet is fired then maybe that's why it doesn't appear?
I don't think so as a tick offset bet will always be reducing your exposure.
I have replied to your email with a question about the diagnostic log. Did you receive it?