As it turns out you should add IPv6 (AAAA) records to your DNS for your S3 bucket also, if you decide to make the Mastodon server available over IPv6. Some mobile clients had issues loading images, since I turned on IPv6. Now with IPv6 on the Mastodon server and the S3 bucket everything runs smoothly again.
INDICATORS OF COMPROMISE (IOC)
InfoSec Community within the Fediverse. Newbies, experts, gurus - Everyone is Welcome! Instance is supposed to be fast and secure.
We have a Getting Started Guide here: https://ioc.wiki/mastodon
HAVE FUN and STAY SAFE!