I don't know if it's because of the way it overrides the chat GUI or if it makes changes to the message text component but itemstack doesn't draw in there.

Quark version: r5-167 (1c49eb9), Chat Tweaks version: 1.12.2-5.1.23

#1354 is still broken in current release.

So support is only given for CF releases then? Great.
I suggest adding that in the https://github.com/Vazkii/Quark/blob/master/CONTRIBUTING.md