1.15.2/1.8 MC crashes after changing versions

WARNING: coremods are present:
Contact their authors BEFORE contacting forge

// I let you down. Sorry

Time: 16.03.20 08:47
Description: Exception in server tick loop

java.lang.NullPointerException: Exception in server tick loop
    at net.minecraft.nbt.NBTTagCompound.func_152449_a(NBTTagCompound.java:415)
    at net.minecraft.nbt.NBTTagCompound.func_152446_a(NBTTagCompound.java:52)
    at net.minecraft.nbt.NBTTagCompound.func_152449_a(NBTTagCompound.java:415)
    at net.minecraft.nbt.NBTTagCompound.func_152446_a(NBTTagCompound.java:52)
    at net.minecraft.nbt.NBTTagCompound.func_152449_a(NBTTagCompound.java:415)
    at net.minecraft.nbt.NBTTagCompound.func_152446_a(NBTTagCompound.java:52)
    at net.minecraft.nbt.CompressedStreamTools.func_152455_a(CompressedStreamTools.java:134)
    at net.minecraft.nbt.CompressedStreamTools.func_152456_a(CompressedStreamTools.java:89)
    at net.minecraft.nbt.CompressedStreamTools.func_74794_a(CompressedStreamTools.java:84)
    at net.minecraft.world.chunk.storage.AnvilChunkLoader.loadChunk__Async(AnvilChunkLoader.java:117)
    at net.minecraftforge.common.chunkio.ChunkIOProvider.callStage1(ChunkIOProvider.java:20)
    at net.minecraftforge.common.chunkio.ChunkIOProvider.callStage1(ChunkIOProvider.java:12)
    at net.minecraftforge.common.util.AsynchronousExecutor.skipQueue(AsynchronousExecutor.java:343)
    at net.minecraftforge.common.util.AsynchronousExecutor.getSkipQueue(AsynchronousExecutor.java:302)
    at net.minecraftforge.common.chunkio.ChunkIOExecutor.syncChunkLoad(ChunkIOExecutor.java:12)
    at net.minecraft.world.gen.ChunkProviderServer.loadChunk(ChunkProviderServer.java:117)
    at net.minecraft.world.gen.ChunkProviderServer.func_73158_c(ChunkProviderServer.java:92)
    at net.minecraft.server.MinecraftServer.func_71222_d(MinecraftServer.java:302)
    at net.minecraft.server.integrated.IntegratedServer.func_71247_a(IntegratedServer.java:181)
    at net.minecraft.server.integrated.IntegratedServer.func_71197_b(IntegratedServer.java:204)
    at net.minecraft.server.MinecraftServer.run(MinecraftServer.java:438)
    at java.lang.Thread.run(Thread.java:745)

A detailed walkthrough of the error, its code path and all known details is as follows:
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-- System Details --
Details:
    Minecraft Version: 1.8
    Operating System: Windows 10 (amd64) version 10.0
    Java Version: 1.8.0_51, Oracle Corporation
    Java VM Version: Java HotSpot(TM) 64-Bit Server VM (mixed mode), Oracle Corporation
    Memory: 857610920 bytes (817 MB) / 1308622848 bytes (1248 MB) up to 2147483648 bytes (2048 MB)
    JVM Flags: 8 total; -XX:HeapDumpPath=MojangTricksIntelDriversForPerformance_javaw.exe_minecraft.exe.heapdump -Xmx2G -XX:+UnlockExperimentalVMOptions -XX:+UseG1GC -XX:G1NewSizePercent=20 -XX:G1ReservePercent=20 -XX:MaxGCPauseMillis=50 -XX:G1HeapRegionSize=32M
    IntCache: cache: 15, tcache: 0, allocated: 13, tallocated: 95
    FML: MCP v9.10 FML v8.0.99.99 Minecraft Forge 11.14.4.1563 Optifine OptiFine_1.8_HD_U_H6 7 mods loaded, 7 mods active
    States: 'U' = Unloaded 'L' = Loaded 'C' = Constructed 'H' = Pre-initialized 'I' = Initialized 'J' = Post-initialized 'A' = Available 'D' = Disabled 'E' = Errored
    UCHIJAA    mcp{9.05} [Minecraft Coder Pack] (minecraft.jar)
    UCHIJAA    FML{8.0.99.99} [Forge Mod Loader] (forge-1.8-11.14.4.1563.jar)
    UCHIJAA    Forge{11.14.4.1563} [Minecraft Forge] (forge-1.8-11.14.4.1563.jar)
    UCHIJAA    imsm{1.8} [Instant Massive Structures Mod] ([1.8]InstantMassiveStructuresMod2.jar)
    UCHIJAA    cfm{4.0.1} [MrCrayfish's Furniture Mod] (cfm-4.0.1-mc1.8(1).jar)
    UCHIJAA    TooMuchTNT{3.0} [TooMuchTNT] (Too-Much-TNT-Mod-1.8.jar)
    UCHIJAA    worldedit{6.1} [WorldEdit] (worldedit-forge-mc1.8-6.1.jar)
    Loaded coremods (and transformers):
    GL info: ~~ERROR~~ RuntimeException: No OpenGL context found in the current thread.
    Profiler Position: N/A (disabled)
    Player Count: 0 / 8; []
    Type: Integrated Server (map_client.txt)
    Is Modded: Definitely; Client brand changed to 'fml,forge'