I had a timer which relied on an AreaEffectCloud's age increasing to run some functions, however, the age stopped changing when I wasn't in the spawn chunks until I teleported back. I then checked on items and the same issue was occurring.
It looks like spawn chunks are only lazy processing chunks in the current snapshot.
 

Expected Behavior

An entity's age should still change in the spawn chunks when there is no player nearby.
Falling blocks should process that they are falling and also increase there Time value.

Current Behavior

An entity's age stops changing in the spawn chunks when not loaded by the player, even if the entity is directly in the center of the spawn chunks.
Falling sand does not get processed (does not fall, Time does not change)

Steps to Reproduce

1. Set the world spawn to 0, 0:
   /setworldspawn 0 0 0
2. Leave the area:
   /tp 10000 ~ ~
3. Summon e.g. a falling block at spawn:
   /summon minecraft:falling_block 0 100 0 {Time:1}
4. Read the entity's NBT
   /data get entity @e[type=minecraft:falling_block,limit=1]

Falling block is still present, it has not started falling yet (Pos:[0.5d, 100.0d, 0.5d])) nor has the the Time tag increased.