Steps to reproduce:

1. Create 2 hosts in the frontend. For ease of reproducing, link the ICMP Ping template to both hosts. Make sure that the items are receiving data in the frontend.
2. Create a network map with 2 elements, one for each of the hosts created in step one
3. Create a link between the 2 elements. In the Label field for the link, try adding an expression macro {?last(/ {HOST.HOST}

   /icmppingsec)}. 

4. Save it. In the network map the link label will not expand to the item value. It will just show the expression macro in step 3. 

Reference doc: https://www.zabbix.com/documentation/current/en/manual/config/visualization/maps/map#linking-elements

The expression macro works fine in the map element label field.