We had a report from a customer that after upgrading from 6.2 to 6.4 they saw that their memory usage had increased drastically, from ~8GB to ~16GB. During troubleshooting we noticed that after disabling the Cisco Meraki template, which has quite a bit of Script items, the memory usage decreased to the previous 8GB.

At first the customer was using 6.2 Cisco Meraki template on a 6.4 installation, and it seemed like there was a memory leak, as the available memory continued to decrease.
Available memory after enabling Cisco Meraki template on the night of 25th:

After upgrading the template to 6.4, the memory usage was still drastically high, but it seems to have stopped growing, leading us to believe there is not a memory leak but simply the memory usage is much higher.
Available memory after enabling updated 6.4 Cisco Meraki template, memory usage stabilises but still is much higher than previous version of Zabbix:

If the Cisco Meraki template is disabled, the memory usage drops by ~8GB.