I encountered new problems upgrading ZM from 1.34 to 1.36 : events wouldn't record because of buffers issues (see settings in Source > Buffers) or they would start but then fill up RAM in seconds.
Turned out to be from my IP cameras which have a setting "Smart Codec" that had to be turned off to let ZM record correctly (to get iframes). source : https://forums.zoneminder.com/viewtopic.php?f=42&t=30481#p120107
Maybe check on your camera