Great. Try reprogram your PIC with the lowest Brown-Out-voltage treshold too. Power-Up timer have to bet set too.

Of course noisy supply line and 'weird contact' on a board can do bad results. PIC18F series are really noise sensitive... use of external pull-ups instead of the internal seems to solve some problems. After some tests, Pull-ups lower than 4.7k give better result. i use 1K in all my apps. For sure sink a bit more current but... it works.