current 1.12.2 server:
https://launcher.mojang.com/mc/game/1.12.2/server/886945bfb2b978778c3a0288fd7fab09d315b25f/server.jar

recommended forge:
https://files.minecraftforge.net/maven/net/minecraftforge/forge/1.12.2-14.23.5.2768/forge-1.12.2-14.23.5.2768-installer.jar

only mods:
Biome_Bundle-1.12.2-v6.1.jar
OpenTerrainGenerator-1.12.2+-+v6.jar

server.properties:
level-type=OTG
level-name=Biome Bundle
level-seed=112358

clean recreated world

stop command still works but cannot parse help or '?'

server works otherwise - no crash after exception - all attempts to get to help texts yield same result

help
[20:46:11] [Server thread/INFO] [minecraft/DedicatedServer]: An unknown error occurred while attempting to perform this command
[20:46:11] [Server thread/WARN] [minecraft/CommandHandler]: Couldn't process command: help
java.lang.IllegalArgumentException: Comparison method violates its general contract!
at java.util.ComparableTimSort.mergeHi(ComparableTimSort.java:866) ~[?:1.8.0_191]
at java.util.ComparableTimSort.mergeAt(ComparableTimSort.java:483) ~[?:1.8.0_191]
at java.util.ComparableTimSort.mergeForceCollapse(ComparableTimSort.java:422) ~[?:1.8.0_191]
at java.util.ComparableTimSort.sort(ComparableTimSort.java:222) ~[?:1.8.0_191]
at java.util.Arrays.sort(Arrays.java:1312) ~[?:1.8.0_191]
at java.util.Arrays.sort(Arrays.java:1506) ~[?:1.8.0_191]
at java.util.ArrayList.sort(ArrayList.java:1462) ~[?:1.8.0_191]
at java.util.Collections.sort(Collections.java:141) ~[?:1.8.0_191]
at net.minecraft.command.CommandHelp.func_184900_a(SourceFile:116) ~[cn.class:?]
at net.minecraft.command.CommandHelp.func_184881_a(SourceFile:71) ~[cn.class:?]
at net.minecraft.command.CommandHandler.func_175786_a(CommandHandler.java:119) [bj.class:?]
at net.minecraft.command.CommandHandler.func_71556_a(CommandHandler.java:91) [bj.class:?]
at net.minecraft.server.dedicated.DedicatedServer.func_71333_ah(DedicatedServer.java:433) [nz.class:?]
at net.minecraft.server.dedicated.DedicatedServer.func_71190_q(DedicatedServer.java:398) [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(Thread.java:748) [?:1.8.0_191]