Hows Cache Burst value generated? Can collisions happen?

Hi. Our load balancer caches certain page resourses and sometimes we receive outdated payload cached from a previous app deploy.  To get an up-to-date version it’s enough to change the cache burst value in the resource URL: some?637945052630427850 So it seems that the previous app package had the same cache burst value. But how is it possible? What’s this number “637945052630427850” anyway? It doesn’t look like seconds since epoch.  
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