F3+T = Reloads current resource pack (will lag)
F3+S = I forgot what this does, but it is a resource demanding debug feature
F3+A = Reloads loaded chunks
All of these are intended to cause said lag spikes.
World Border in Nether = This might not be intended
This happens on servers that use the method of putting ยง in front of names. To re-create try servers like us.mineplex.com and mc.hypixel.com
Luke Ruggiero
F3+T = Reloads current resource pack (will lag)
F3+S = I forgot what this does, but it is a resource demanding debug feature
F3+A = Reloads loaded chunks
All of these are intended to cause said lag spikes.
World Border in Nether = This might not be intended