When trying to create some simple custom splines, I am able to load my pack without any warnings. The world loads to 100% and then freezes on that screen. Thereafter I have to use task manager to close the program, and the game output never registers any error.
The pack attached below demonstrates the problem.
Please check if this is still an issue for you in 1.19.4 or later. If so, please provide an updated data pack that works with the most recent version of Minecraft.