The rumours that Raab would resign if the ‘backstop’ didn’t have a specific time limit were circulating back since Nov 5th - here is just one of the many sites that reported this:
There was no denial re the time limit from Raab, so the market waited.
The talk from EU was that there would be no time limit so many traders were cautious going long GBP when the agreement was published.
Note how ‘contained’ Eur/Gbp was when Irish broadcaster RTE reported a leak that a draft was agreed (Nov 13 at 15.55gmt) - maybe that move caused your crossover.
Next day - no time limit and no resignation - cabinet meeting announced for 14.00gmt - see again the containment - that was the time to exit.
Crossovers are great - but important to be market aware.