Thumbnail caching doesn't work when plugin is enabled

When the plugin is enabled and the following configuration is set, there are no thumbnail files generated on S3 or the local filesystem.

Turning off the extension results in thumbnails being generated on the local files system.

AWS permissions are fully open to the bucket, I even gave the IAM user full administrator access temporarily just to test it just in case it was a permission issue.

I'm also getting the error Unable to write to upload destination. Check permissions on (useful isn't it) when uploading files via the Bolt file manager.

app/config/extensions/amazon.jarjak.yml

enabled: 1
client_version: 'latest'
bucket_region: eu-west-2
bucket_name: thebucketimusing
filesystem_prefix: ''
filesystem_name: 'files'
file_list_limit: 1000
cache_ttl: 3600
use_redis: 1

# Already configured via config.yml session key
redis_host:
redis_port:
redis_prefix:

The following settings are enabled for my bolt config:

base_url: http://dev.theurl.co.uk
env: dev
debug: true
debug_show_loggedoff: true

caching:
  config: false
  templates: false
  request: false
  thumbnails: true # Note this value
  translations: false

thumbnails:
  save_files: true # Note this value

debug_error_level: 8181   # error level when debug enabled
production_error_level: 0 # error level when debug disabled

debuglog:
  enabled: true

Bolt version: 3.7 (downgraded to 3.5 and also experiencing the same)

JarJak / bolt-amazon

Thumbnail caching doesn't work when plugin is enabled #5