Misconfiguration of routing, say for example, with Router A being connected to a peering exchange, but Router A not having 'redistribute connected' configured in BGP, will end up with Router B having no path to the nexthop for those routes, as peering-exchanges generally do not publicly advertise their prefixes. This causes the routes learnt from the peering exchange to be invalid on Router B, which in turn seems to cause an update storm and results in all memory being quickly consumed by Zebra and it crashing.
Setting a static route for the prefix of the peering exchange toward Router A resolved the condition.