Learn more about this change here.
For help regarding Aternos, we recommend you to visit our support center.
Welcome to the world of mods. i have had some success on my own, by having another user keep the chunk a player is in loaded, when he joins. Try that. If not Share Your logs from when it happens here please.
1.) Go to your log on Aternos: https://aternos.org/log/
2.) Click on the big blue "Share" button on the top right
3.) Copy the link with (Ctrl + C or click on the "Copy" button)
4.) Send the link here.
Scroll to the bottom, almost, the red text there tells you it is an entity named GHAST that has an error, and that causes it to stop. I would suggest trying to start the server, do NOT join, but in console on the website for Your server, type /kill @e[type=ghast] That should kill ALL ghasts.
Change from Vanilla server to PaperMC. 1.13.x servers have had a BIG tehcnical update, and they are extremely resource-intensive and even if you will still feel the effects of that even after the Aternos Team has increased the availible Resources/RAM for all 1.13.2 servers, paperMC atleast runs it a little bit better.
Well, information about that, then. Its a pretty common misconception among players in discord, that when they change it there, its immidate. Just like typing it in console or as a command ingame
Something like this, in Big, friendly letters ofcourse 
No. You have not. This is a free service. You are probably running plugins/mods, and its just too many of them for the server to handle. Also. There is different types of "lag" so make sure its not just Your Connection to the server that is poor.
[Server thread/ERROR] [net.minecraft.server.MinecraftServer]: Encountered an unexpected exception
4996
java.lang.OutOfMemoryError: Metaspace
4997
[09:17:03] [Server thread/INFO] [net.minecraft.server.MinecraftServer]: Stopping server
4998
[09:17:34] [Server thread/ERROR] [net.minecraft.server.MinecraftServer]: Exception stopping the server
4999
java.lang.OutOfMemoryError: Metaspace
Tells you that it ran out of memory. Stoneblock2 is a Heavy mod. You might not be able to launch it every single time, especially when the servers are busy(the Queue for starting is long)
As far as I know, this limit is technical, and the Aternos Team is unable to change it.
A few configuration options on the webinterface for the servers need you to stop the server to implement changes. Could save a few questions from users if this were clearer on those pages.
Are atleast two pages where it would be nice to clearify for the users. that the server needs to be stopped to do changes/backup.
