Problem
Your builds fail due to Tasks for AWS seemingly being not installed, for example:
Could not execute task 'Download artifacts' no Plugin with key 'net.utoolity.atlassian.bamboo.tasks-for-aws:aws.s3.object' is installed.
Cause
Some Bamboo versions do not pick up changes to tasks after updating an app:
This long standing upstream issue had been resolved as of Bamboo 5.3 (unfortunately without sharing the exact cause to help assessing whether the workarounds below depend on other conditions). However, there seems to be a regression for Bamboo versions 5.6+, which expose a similar defect.
Workarounds
If an upgrade to Bamboo >= 5.3 is not desired or possible currently, the issue mentions two eventual workarounds:
restarting the Bamboo server
Unfortunately both methods are contested to work reliably, notably Martin Reinhold qualifies this to feel like Russian roulette.