I don't think this is fixed, as suggested in ZBX-2461. Just tried an import in pre-zabbix-1.8.3.x-12366, got the same error again while adding a trigger that checks on port 3000 via TCP.

"Not allowed symbols or sequence of symbols in expression element detected: Check expression part starting from 'tcp,3000.avg(600)}=0'"

Trigger details from import:

<trigger>
<description>CASP</description>
<type>0</type>
<expression>{{HOSTNAME}:tcp,3000.avg(600)}=0</expression>
<url></url>
<status>0</status>
<priority>4</priority>
<comments></comments>
</trigger>

Also tried a stripped down version of my import, as it is quite large, and I have the same issue.