Well, first I found out the server didn't start up completely, you can look at in the "logs" folder for the "latest" text document and see when your server has started completely. I've uploaded a log file for example for my server. When you open up the log file you will maybe need to restart it (close it and double click on it again) to see new things added to the log file. If your server lags by any chance and you are sure your internet is NOT the problem ,go to task manager and look at the CPU usage, watch out because if it's 100% that's bad. A new Forge version for 1.12.2 has been released (14.23.4.2739). If you have any other questions, just ask me. ?
latest.log The server will never show anything, maybe they will fix it eventually,so you will just have to look at the log file to see when it starts etc. But you can still put commands in the console and they will work, like "op [player name]".