I also have this issue. The chunks will finally load in but they tend to fill in randomly and not closest to the player. This current server was 1.13.2 fresh install upgraded to 1.14. My hardware is nothing impressive but 1.13.2 never did this and actually ran quite smoothly.
Also if I'm traveling too quickly and rendering new chunks it causes massive server lag spikes which may or may not be related to this issue.
Exploring new areas in a boat is something we've noticed that brings the server to it's knees. Full stop while chunks randomly load very slow all around. Gotta just wait it out. Another oddity is there will be times that I can place blocks and break them and get that immediate pop sound as the block breaks and immediately goes into my inventory... everything feels perfectly fine but I can't eat unless I hold the mouse button down for a long period of time. And there are times where it never registers that I've eaten.
The only way we can play with minimal lag spikes is to all stay very close together very few chunks apart.