This has been a bug since early March 2019. Still not resolved.
Trader Llamas are supposed to defend the Wandering Trader from zombies and other hostile mobs. Currently they do nothing.
Tamed Trader Llamas would also defend villages from zombies and illagers. Now they are passive.
Thank you for your report!
We're actually already tracking this issue in MC-146805, so I resolved and linked this ticket as a duplicate.
If you would like to add a vote and any extra information to the main ticket it would be appreciated.
If you haven't already, you might like to make use of the search feature in the future to see if the issue has already been reported.
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