If shaders are enabled, the message "[LWJGL] OpenGL debug message" will be printed to the log every frame with no additional information. This may be caused by an outdated version of Iris, though I can't confirm this as using the latest 1.18.2 version of Iris (1.6.4 as of the time of writing) causes a crash on startup.

Have got iris + flywheel compat updated on my dev build and this error seems to no longer appear, i'll wait & verify for a little longer to see if that was indeed the solution.