On my server, I'd like to use the latest version of all the quests, but /bq_admin default load doesn't seem to be working. None of the new quests are showing up, it just reset all the progressed quests to uncompleted. This is on version 3.5.296.

Build 3.4.158 of Standard Expansion is now up on Curse with a fix included for this. There's also build 3.5.299 of Better Questing available too.

Is there any additional error information in the server logs after the command was attempted?

Here's what the server log says when I try to execute the command: https://hastebin.com/ozomafiwok.sql

Found it... actually a bug in the Standard Expansion, specifically taming tasks. I'll try and get a build out later today to fix that