Hello. Recently I've had problems with my server, as I updated it to the newest version to test it. There was much internal lag, and later I noticed there wasn't OptiFine yet for the 1.13, so I downgraded it to 1.12. When I did this, the server couldn't start for errors mclo.gs couldn't detect, later I read this in the Minecraft forum:
<<The world save format has changed; worlds older than 1.13 cannot be opened with versions from 1.13 or later without permanently and irreversibly upgrading them to the new format, making it impossible to open them in earlier versions>>
Luckily I made a backup before upgrading, but I want you to be aware before upgrading: make a backup before or you won't be able to downgrade.
I know this isn't a question (and maybe it's in the wrong category) but I think this is important for all Aternos users who want to upgrade to 1.13.
