I seem to be unable to join the GTM server 1, I have a feeling it may be because there are so many people online as I have checked my Wifi multiple times and have tried logging onto other servers with no issues. This is a good problem to have I suppose as it shows the server is growing. I would suggest upgrading the server so that it can hold more people and still run smoothly.
This is not a problem I have been hearing about. What you should do is to not use 1.13 if you were and use 1.9-1.12.2 instead. Also, you should download the resource pack and then disable resource packs for GTM. Also, could you tell me your in game name?