Server property generator-settings does not work with any value

Generator configuration from server.properties:

level-type=flat
generator-settings={"biome":"minecraft:plains","layers":[{"block":"minecraft:air","height": 1}],"structures":{"structures":{}}}

On server startup appears this error:

[main/ERROR] Not a registry ops

Then server proceed boot normally and uses default flat world generator settings.

Full server log:

Picked up _JAVA_OPTIONS: -Dawt.useSystemAAFontSettings=on -Dswing.aatext=true 
[21:15:24] [main/ERROR]: Not a registry ops 
[21:15:24] [main/INFO]: Environment: authHost='https://authserver.mojang.com', accountsHost='https://api
.mojang.com', sessionHost='https://sessionserver.mojang.com', name='PROD' 
[21:15:24] [main/WARN]: Ambiguity between arguments [teleport, destination] and [teleport, targets] with
 inputs: [Player, 0123, @e, dd12be42-52a9-4a91-a8a1-11c01849e498] 
[21:15:24] [main/WARN]: Ambiguity between arguments [teleport, location] and [teleport, destination] wit
h inputs: [0.1 -0.5 .9, 0 0 0] 
[21:15:24] [main/WARN]: Ambiguity between arguments [teleport, location] and [teleport, targets] with in
puts: [0.1 -0.5 .9, 0 0 0] 
[21:15:24] [main/WARN]: Ambiguity between arguments [teleport, targets] and [teleport, destination] with
 inputs: [Player, 0123, dd12be42-52a9-4a91-a8a1-11c01849e498] 
[21:15:24] [main/WARN]: Ambiguity between arguments [teleport, targets, location] and [teleport, targets
, destination] with inputs: [0.1 -0.5 .9, 0 0 0] 
[21:15:24] [main/INFO]: Reloading ResourceManager: Default 
[21:15:25] [Worker-Main-10/INFO]: Loaded 7 recipes 
[21:15:25] [Worker-Main-10/INFO]: Loaded 927 advancements 
[21:15:26] [Server thread/INFO]: Starting minecraft server version 1.16.2 
[21:15:26] [Server thread/INFO]: Loading properties 
[21:15:26] [Server thread/INFO]: Default game type: SURVIVAL 
[21:15:26] [Server thread/INFO]: Generating keypair 
[21:15:26] [Server thread/INFO]: Starting Minecraft server on *:25565 
[21:15:26] [Server thread/INFO]: Using epoll channel type 
[21:15:26] [Server thread/INFO]: Preparing level "world" 
[21:15:26] [Server thread/INFO]: Preparing start region for dimension minecraft:overworld 
[21:15:27] [Server thread/INFO]: Preparing spawn area: 0% 
[21:15:27] [Server thread/INFO]: Preparing spawn area: 0% 
[21:15:27] [Server thread/INFO]: Preparing spawn area: 0% 
[21:15:28] [Server thread/INFO]: Preparing spawn area: 39% 
[21:15:29] [Worker-Main-12/INFO]: Preparing spawn area: 83% 
[21:15:29] [Worker-Main-10/INFO]: Preparing spawn area: 83% 
[21:15:29] [Worker-Main-12/INFO]: Preparing spawn area: 83% 
[21:15:29] [Worker-Main-11/INFO]: Preparing spawn area: 83% 
[21:15:30] [Worker-Main-9/INFO]: Preparing spawn area: 83% 
[21:15:30] [Worker-Main-9/INFO]: Preparing spawn area: 83% 
[21:15:31] [Worker-Main-8/INFO]: Preparing spawn area: 83% 
[21:15:31] [Worker-Main-14/INFO]: Preparing spawn area: 87% 
[21:15:32] [Worker-Main-14/INFO]: Preparing spawn area: 91% 
[21:15:32] [Server thread/INFO]: Preparing spawn area: 98% 
[21:15:33] [Server thread/INFO]: Time elapsed: 6638 ms 
[21:15:33] [Server thread/INFO]: Done (6.690s)! For help, type "help"