How far off is it (your current max)?
And the was the 405 hit? If it was a long time ago then it is likely that you lost some strength and that you are not the same as you were. Contest attempts and goals should never be made based on an all time best that you might have done once on a magical day. Goals and attempts should be made based on what you consistently make in the gym.
If the 405 wasn't done too long ago AND you hit it on several occasions then you might be overworked.... the pressure of a contest can easily have you do too much and your performance drops.
If its the second case the best thing is NOT to test yourself in the gym and to do LESS actual deadlift work and more mon stressful assitance work for the muscles involved in the deadlift.
If it is the second case you need to re-evaluate your goals for the competition.
It also depends on how far you are...if you are 30-40lbs away you wont gain that in 2 weeks. If you are 10lbs away you can do it if you dont burn out.
Anyway, the adrenalin of the contest should give you a 10lbs boost
And again, what you hit once in your life doesn't count. As long as you don't hit it on 3 separate occasions I would not trust it as a max to base your contest prediction on.
I see that a lot with crossfitters. They hit a 225 snatch once after missing it 20 times the previous month and then use it to plan their loads in training whereas their real solid max might be 205. So they end up using too much weight in training an having bad technique and missing lifts.
BUT more likely than not, your nervous system is starting to show signs of fatigue. The deadlift is the most "neural" of the strength lifts. I know what it is like to prepare for a contest.. you want to do well so bad that you go too hard too often and you lose your neural drive and your perform like an arse. This is especially common when you don't have much competition experience... STOP going all out on the deadlift... work on form and speed more than maximum weights. Stick to doubles at 80-90% (most in 80-85% zone) and do a LITTLE heavy work from pins (e.g. sets of 2 pin pull from below knees with 405-425 just to keep the feeling of a heavy weight,,, DO NOT GO TOO HEAVY....DO NOT MAKE THIS INTO A MAX EFFORT OR DO TOO MUCH VOLUME.... 2 or 3 x 2 is enough).