Since the launch of BBM 10.3 on BlackBerry 10 we have been hearing from select users running into issues. It seems like there is an issue with the latest BBM and any device running a variant of 10.2.1 older than 10.2.1.1975. I am still trying to see if there is anything official from BlackBerry on this but the best bet it to upgrade to a new OS. I personally recommend the 10.2.1.2141 variant that is available now that Vodafone officially released it.
My guess is that BlackBerry will probably put out an update to fix the issue once they nail it down.