Modded world will not get past loading world stage without crashing

So I was trying to add a mod that I made into Minecraft and I made a new world for it. It loads until 100%, but it then crashes with the following crash report:

---- Minecraft Crash Report ----
// I feel sad now :(

Time: 09/05/20 20:11
Description: Ticking memory connection

java.lang.RuntimeException: Why did the advancements not load yet?!
    at net.minecraftforge.common.AdvancementLoadFix.loadVisibility(AdvancementLoadFix.java:51) ~[?:?] {re:classloading}
    at net.minecraft.advancements.PlayerAdvancements.func_192740_f(PlayerAdvancements.java:157) ~[?:?] {re:classloading}
    at net.minecraft.advancements.PlayerAdvancements.<init>(PlayerAdvancements.java:65) ~[?:?] {re:classloading}
    at net.minecraft.server.management.PlayerList.func_192054_h(PlayerList.java:749) ~[?:?] {re:classloading}
    at net.minecraft.entity.player.ServerPlayerEntity.<init>(ServerPlayerEntity.java:164) ~[?:?] {re:classloading,pl:accesstransformer:B}
    at net.minecraft.server.management.PlayerList.func_148545_a(PlayerList.java:382) ~[?:?] {re:classloading}
    at net.minecraft.network.login.ServerLoginNetHandler.func_147326_c(ServerLoginNetHandler.java:116) ~[?:?] {re:classloading}
    at net.minecraft.network.login.ServerLoginNetHandler.func_73660_a(ServerLoginNetHandler.java:63) ~[?:?] {re:classloading}
    at net.minecraft.network.NetworkManager.func_74428_b(NetworkManager.java:224) ~[?:?] {re:classloading}
    at net.minecraft.network.NetworkSystem.func_151269_c(NetworkSystem.java:135) ~[?:?] {re:classloading}
    at net.minecraft.server.MinecraftServer.func_71190_q(MinecraftServer.java:866) ~[?:?] {re:classloading,pl:accesstransformer:B}
    at net.minecraft.server.MinecraftServer.func_71217_p(MinecraftServer.java:784) ~[?:?] {re:classloading,pl:accesstransformer:B}
    at net.minecraft.server.integrated.IntegratedServer.func_71217_p(IntegratedServer.java:114) ~[?:?] {re:classloading,pl:runtimedistcleaner:A}
    at net.minecraft.server.MinecraftServer.run(MinecraftServer.java:637) [?:?] {re:classloading,pl:accesstransformer:B}
    at java.lang.Thread.run(Thread.java:745) [?:1.8.0_74] {}

A detailed walkthrough of the error, its code path and all known details is as follows:
---------------------------------------------------------------------------------------

-- Head --
Thread: Server thread
Stacktrace:
    at net.minecraftforge.common.AdvancementLoadFix.loadVisibility(AdvancementLoadFix.java:51)
    at net.minecraft.advancements.PlayerAdvancements.func_192740_f(PlayerAdvancements.java:157)
    at net.minecraft.advancements.PlayerAdvancements.<init>(PlayerAdvancements.java:65)
    at net.minecraft.server.management.PlayerList.func_192054_h(PlayerList.java:749)
    at net.minecraft.entity.player.ServerPlayerEntity.<init>(ServerPlayerEntity.java:164)
    at net.minecraft.server.management.PlayerList.func_148545_a(PlayerList.java:382)
    at net.minecraft.network.login.ServerLoginNetHandler.func_147326_c(ServerLoginNetHandler.java:116)
    at net.minecraft.network.login.ServerLoginNetHandler.func_73660_a(ServerLoginNetHandler.java:63)
    at net.minecraft.network.NetworkManager.func_74428_b(NetworkManager.java:224)

-- Ticking connection --
Details:
    Connection: net.minecraft.network.NetworkManager@5e9afe63
Stacktrace:
    at net.minecraft.network.NetworkSystem.func_151269_c(NetworkSystem.java:135)
    at net.minecraft.server.MinecraftServer.func_71190_q(MinecraftServer.java:866)
    at net.minecraft.server.MinecraftServer.func_71217_p(MinecraftServer.java:784)
    at net.minecraft.server.integrated.IntegratedServer.func_71217_p(IntegratedServer.java:114)
    at net.minecraft.server.MinecraftServer.run(MinecraftServer.java:637)
    at java.lang.Thread.run(Thread.java:745)

-- System Details --
Details:
    Minecraft Version: 1.15.2
    Minecraft Version ID: 1.15.2
    Operating System: Mac OS X (x86_64) version 10.15.4
    Java Version: 1.8.0_74, Oracle Corporation
    Java VM Version: Java HotSpot(TM) 64-Bit Server VM (mixed mode), Oracle Corporation
    Memory: 1422777888 bytes (1356 MB) / 2147483648 bytes (2048 MB) up to 2147483648 bytes (2048 MB)
    CPUs: 4
    JVM Flags: 8 total; -Xss1M -Xmx2G -XX:+UnlockExperimentalVMOptions -XX:+UseG1GC -XX:G1NewSizePercent=20 -XX:G1ReservePercent=20 -XX:MaxGCPauseMillis=50 -XX:G1HeapRegionSize=32M
    ModLauncher: 5.1.0+69+master.79f13f7
    ModLauncher launch target: fmlclient
    ModLauncher naming: srg
    ModLauncher services: 
        /eventbus-2.1.0-service.jar eventbus PLUGINSERVICE 
        /forge-1.15.2-31.1.50.jar object_holder_definalize PLUGINSERVICE 
        /forge-1.15.2-31.1.50.jar runtime_enum_extender PLUGINSERVICE 
        /accesstransformers-2.1.1-shadowed.jar accesstransformer PLUGINSERVICE 
        /forge-1.15.2-31.1.50.jar capability_inject_definalize PLUGINSERVICE 
        /forge-1.15.2-31.1.50.jar runtimedistcleaner PLUGINSERVICE 
        /forge-1.15.2-31.1.50.jar fml TRANSFORMATIONSERVICE 
    FML: 31.1
    Forge: net.minecraftforge:31.1.50
    FML Language Providers: 
        javafml@31.1
        minecraft@1
    Mod List: 
        forge-1.15.2-31.1.50-client.jar Minecraft {minecraft@1.15.2 DONE}
        And Then It Began 1.15.2.jar And Then It Began {andthenitbegan@1.0.0 DONE}
        forge-1.15.2-31.1.50-universal.jar Forge {forge@31.1.50 DONE}
        worldedit-forge-mc1.15.2-7.1.0.jar WorldEdit {worldedit@7.1.0;48cc31c DONE}
    Player Count: 0 / 8; []
    Data Packs: vanilla, mod:andthenitbegan, mod:forge (incompatible), mod:worldedit (incompatible)
    Type: Integrated Server (map_client.txt)
    Is Modded: Definitely; Client brand changed to 'forge'

Can't seem to get it to load the world. Please help!