By "deeply unpredictable", they mean 'we're waiting on the Israeli exit polls but if he gets back, it's really, really predictable; we just can't say it right now'.
In its updated advice, the UK Foreign Office described the situation as “deeply unpredictable” (previously “unpredictable”) and said the risk of sudden escalation was high, replacing earlier language about possible further attacks and unforeseen escalation. www.gov.uk/foreign-trav...