Intermittent outside connectivity but connections work locally?

I'm running apache on an AWS server and I have an issue that I can't find any answers to. Normally I'd trawl through this site until something similar crops up and work with that but I can find literally nothing on this:

• Apache 2.4 running on AWS Windows 2012
• Listening on port 443 correctly
• Everything works fine

Something goes wrong.

• Apache cannot be accessed outside of the server
• Apache is available locally on port 443
• Apache is still listening on port 443
• No new TCP connections are being established to the server from the outside world.

With the above information, anyone would think that the issue is with the AWS server but it isn't..

Bouncing the Apache 2.4 service on the AWS server corrects the issue and allows connections in from the outside world.

I'd really appreciate some help with this one.. it's been driving me crazy!

Thanks

Will