Welcome to the forums:
You are most likely encountering a phenomenon known as
simulcast distortion, perhaps the most discussed issue on these forums while trying to monitor this system. In a simulcast system, a site is not a single transmitter at a specific location, but rather a collection of transmitters spread out over a certain area that all transmit on the same frequency at the same time. It's all those signals coming to your scanner at the same time that cause most scanners to lock up, stutter, miss transmissions, etc. Ultimately the only scanners designed to mitigate the effects of simulcast distortion are the Uniden SDS100 (portable) or SDS200 (base). Yes they are the most expensive but they do the job right. There are a number of workarounds for other scanners mentioned in the wiki I linked but they work in very few cases.
