When loading chunks in 19w37a, chunk rendering is much slower than it was in 1.14.4. When you go into an unloaded chunk, you also receive a lag spike that lags out both the client and the server, making it really hard to explore the world via elytra due to framerate and performance drops. To reproduce, fly around on elytra and notice that chunk loading is slower and often causes lag spikes in 19w37a when it doesn't in 1.14.4. My debug report was made when I was flying during a lag spike in 19w37a.