Nextcloud AWS instance SSH problems

I have an AWS instance that I use as a nextcloud server (running version 17.1). Everything was fine for the first ten days or so, but now if I try to log in to the instance using SSH or try to access the instance through the nextcloud client on my phone, my connection just times out.

According to the support documents, if I run -

AWS Systems Manager -> Automation -> Execute -> AWSSupport-TroubleshootSSH

It fixes the problem temporarily and I am able to log in and nextcloud works as well. But after a few hours if I try to log back into the instance, I am again unable to do so. How do I go about finding what is causing the problem? I am not sure where to start looking.

Thanks