Multiplayer Mode Impacting New Spawns - As in , they're not spawning at all anymore

This is a long-lived world, spawned in 1.14 so I am leery of anything new.  Within the past few days, while playing in multiplayer, no new spawns occur.

Switching off multiplayer seems to help temporarily, but nothing we do seems to help.

What's going on?

World is too large to attach.  https://drive.google.com/file/d/1EODNiov7pS7SBCZJlZIZrW_S2nWp_l1_/view?usp=sharing