What you probably want:
https://github.com/Draco18s/ReasonableRealism/blob/1.12.1/src/main/java/com/draco18s/hardlib/client/ClientEasyRegistry.java#L102
For sate-based items where each state has a different item (wood type, wool color, etc):
https://github.com/Draco18s/ReasonableRealism/blob/1.12.1/src/main/java/com/draco18s/hardlib/client/ClientEasyRegistry.java#L70
So if you are tired of modding and don't enjoy it, why do it. If you're frustrated thats understandable but please, if you do not enjoy doing something, don't do it.
I can't offer help because I am not very experienced in modding but, that is the only advice I can give to you.
So it is definitely not your connection to the server. The Issue seems to be something else. Your hardware should be more than capable of running this but even the best hardware is vulnerable to software bugs. I don't know what to tell you other than removing all the mods from your client and the server and connect to the server with only forge installed. Then if your issue goes away add the mods back one by one until you experience the issues again and that mod will be causing the issue. This can be an annoying process but it is a last resort.
Hope I helped