Summary

When viewing a ticket in Safari 11.1.2 on macOS 10.13.6, it will use significant CPU even after the page has finished loading

Steps to Reproduce

Opens two pages in a instance and check the Activity Monitor.
The page in focus on Saffari will have it's using around 10%.
If you change them, the activity will vary between them.

Expected: Not have that much of usage by the browser.

Actual: The focus page uses around 10% of the CPU.

Workaround

Use another browser seems to be a good option.