Found another report of this bug for 1.8 that was listed as resolved, so the issue was never fixed or has returned. Mobs will spawn at max world height even if it is daytime. See screenshots.
MC-164493
Hostile mobs spawn at max world height regardless of light level
Resolved
Duplicate
0
Steven James Smith
(Unassigned)
Unconfirmed
(Unassigned)
mob, multiplayer, server
1.14.4
Retrieved
Thank you for your report!
We're actually already tracking this issue in MC-68565, so I resolved and linked this ticket as a duplicate.
However, that ticket has already been resolved as Fixed. The fix will arrive in the next version or is already included in the latest development version of the game.
If you haven't already, you might like to make use of the search feature in the future to see if the issue has already been reported.
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