Pretty simple; the console is spammed with the below message (every frame, from what I can tell) while R is being held to open the toolbelt menu.

[21:21:41] [Client thread/ERROR]: ########## GL ERROR ##########
[21:21:41] [Client thread/ERROR]: @ Render
[21:21:41] [Client thread/ERROR]: 65539: Invalid key -1

Versions

did you solve this? I seem to have gotten a similar report here https://github.com/RobertSkalko/Mine-and-Slash/issues/95 for my mod.

I have not been able to reproduce this.

I just found the issue:
new KeyBinding("key.toolbelt.cycle.left", -1, "key.toolbelt.category"));
This line is causing the error. Setting the keybinding to -1 seems to cause the GL error.

Huh.... Did I not change that already...? Maybe I never pushed a fix...

v1.14.1 for 1.15.2 should fix this log spam.
Turns out GLFW in certain platforms doesn't like me calling InputMappings.isKeyDown for an unassigned keybind.

I'll take a look, but I don't recall it happening in my development environment. Just in case, what OS/GPU/Driver version?

Yeah, it could be to do with other mods, too. I'll test if that is the case if you can't reproduce it.
OS is Windows 10 Pro v1803
GPU is Gigabyte GTX 1060 with Driver 431.60