unfortunately it happens again, but with another error :c
and the problem is the same: i'm trying to log in as the second player on my server. it does not happen when there's only one player online (or maybe it's less frequent)

[03:25:41] [Server thread/ERROR] [minecraft/MinecraftServer]: Encountered an unexpected exception
net.minecraft.util.ReportedException: Exception ticking world
at net.minecraft.server.MinecraftServer.func_71190_q(MinecraftServer.java:762) ~[MinecraftServer.class:?]
at net.minecraft.server.dedicated.DedicatedServer.func_71190_q(DedicatedServer.java:397) ~[nz.class:?]
at net.minecraft.server.MinecraftServer.func_71217_p(MinecraftServer.java:668) ~[MinecraftServer.class:?]
at net.minecraft.server.MinecraftServer.run(MinecraftServer.java:526) [MinecraftServer.class:?]
at java.lang.Thread.run(Unknown Source) [?:1.8.0_211]
Caused by: java.lang.NoSuchMethodError: net.minecraft.block.Block.func_180664_k()Lnet/minecraft/util/BlockRenderLayer;
at net.minecraft.block.Block.canRenderInLayer(Block.java:2159) ~[aow.class:?]
at com.creativemd.littletiles.common.tiles.LittleTileBlock.updateTranslucent(LittleTileBlock.java:131) ~[LittleTileBlock.class:?]
at com.creativemd.littletiles.common.tiles.LittleTileBlock.isTranslucent(LittleTileBlock.java:126) ~[LittleTileBlock.class:?]
at com.creativemd.littletiles.common.tiles.LittleTileBlock.doesProvideSolidFace(LittleTileBlock.java:286) ~[LittleTileBlock.class:?]
at com.creativemd.littletiles.common.tileentity.TileEntityLittleTiles$SideSolidCache.calculateState(TileEntityLittleTiles.java:934) ~[TileEntityLittleTiles$SideSolidCache.class:?]
at com.creativemd.littletiles.common.tileentity.TileEntityLittleTiles$SideSolidCache.calculate(TileEntityLittleTiles.java:922) ~[TileEntityLittleTiles$SideSolidCache.class:?]
at com.creativemd.littletiles.common.tileentity.TileEntityLittleTiles$SideSolidCache.get(TileEntityLittleTiles.java:978) ~[TileEntityLittleTiles$SideSolidCache.class:?]
at com.creativemd.littletiles.common.blocks.BlockTile.isSideSolid(BlockTile.java:457) ~[BlockTile.class:?]
at net.minecraft.block.Block.canCreatureSpawn(Block.java:1357) ~[aow.class:?]
at net.minecraft.world.WorldEntitySpawner.canCreatureTypeSpawnBody(WorldEntitySpawner.java:244) ~[anb.class:?]
at net.minecraft.entity.EntityLiving$SpawnPlacementType.canSpawnAt(EntityLiving.java:1463) ~[vq$a.class:?]
at net.minecraft.world.WorldEntitySpawner.func_180267_a(WorldEntitySpawner.java:226) ~[anb.class:?]
at net.minecraft.world.WorldEntitySpawner.func_77192_a(WorldEntitySpawner.java:754) ~[anb.class:?]
at net.minecraft.world.WorldServer.func_72835_b(WorldServer.java:203) ~[oo.class:?]
at net.minecraft.server.MinecraftServer.func_71190_q(MinecraftServer.java:756) ~[MinecraftServer.class:?]
... 4 more
[03:25:41] [Server thread/ERROR] [minecraft/MinecraftServer]: This crash report has been saved to: D:\katacraft\katabaserver-1.12.2.\crash-reports\crash-2019-12-31_03.25.41-server.txt

upd: it may be related to WorldEdit //stack or //copy commands, because now it happens even when i'm alone on the server, after some time from using these commands.

Sorry again, the method I used was available on server side but called another method which wasn't. Released a new version, now I have made sure it works. Sorry once more for the trouble.