Error: invalid byte sequence in UTF-8 {:level=>:error}

Hi there.
It has been working for several months now without any issues, and now suddenly got into this: Error: invalid byte sequence in UTF-8 {:level=>:error}.
My last editing was adding S3 input to my existing logstash, and that's the one failing.

Here's my input.conf file:
input {
s3 {
type => "loadbalancer"
bucket => "my_bucket"
credentials => ["key", "secret"]
region => "us-east-1"
}
}

Where it will pickup logs from five loadbalancers I have. Again, it was collecting and shipping data normally and it stoped working just like that.

Here's the complete error output:

A plugin had an unrecoverable error. Will restart this plugin.
Plugin: <LogStash::Inputs::S3 type=>"loadbalancer", bucket=>"my_bucket", credentials=>["key", "secret"], region=>"us-east-1", region_endpoint=>"us-east-1">
Error: invalid byte sequence in UTF-8 {:level=>:error}

Let me know if you need any other data and how/when I'll be able to fix this.

Thanks!