Here is the log from when I entered the single-player world onwards:
[15:45:05] [Server thread/INFO]: Syncing config to CykaBlyatGopnik (0048341b-8923-4c5c-9da1-d39f7ac32826)
[15:45:09] [Server thread/INFO]: Saving and pausing game...
[15:45:09] [Server thread/INFO]: Saving chunks for level '1.14.3'/minecraft:overworld
[15:45:09] [Client thread/INFO]: Starting JEI...
[15:45:10] [Client thread/INFO]: Building ingredient list...
[15:45:10] [Client thread/INFO]: Building ingredient list took 3.796 ms
[15:45:10] [Client thread/INFO]: Building ingredient filter...
[15:45:10] [Client thread/INFO]: Building ingredient filter took 598.3 ms
[15:45:10] [Client thread/INFO]: Building bookmarks...
[15:45:10] [Client thread/INFO]: Building bookmarks took 1.697 ms
[15:45:10] [Client thread/INFO]: Building recipe registry...
[15:45:10] [Client thread/INFO]: Building recipe registry took 59.54 ms
[15:45:10] [Client thread/INFO]: Building runtime...
[15:45:10] [Client thread/INFO]: Building runtime took 39.88 ms
[15:45:10] [Client thread/INFO]: Starting JEI took 1.092 s
[15:45:10] [Client thread/FATAL]: Error executing task on Client
io.netty.handler.codec.DecoderException: The received encoded string buffer length is longer than maximum allowed (6 > -8)
at net.minecraft.network.PacketBuffer.func_150789_c(PacketBuffer.java:315) ~[?:?]
at atomicstryker.findercompass.common.network.HandshakePacket.decode(HandshakePacket.java:42) ~[?:1.14.3]
at atomicstryker.findercompass.common.network.NetworkHelper$$Lambda$2096/965454824.apply(Unknown Source) ~[?:?]
at net.minecraftforge.fml.network.simple.IndexedMessageCodec.lambda$tryDecode$0(IndexedMessageCodec.java:106) ~[?:?]
at net.minecraftforge.fml.network.simple.IndexedMessageCodec$$Lambda$4606/1940500689.apply(Unknown Source) ~[?:?]
at java.util.Optional.map(Optional.java:215) ~[?:1.8.0_51]
at net.minecraftforge.fml.network.simple.IndexedMessageCodec.tryDecode(IndexedMessageCodec.java:106) ~[?:?]
at net.minecraftforge.fml.network.simple.IndexedMessageCodec.consume(IndexedMessageCodec.java:147) ~[?:?]
at net.minecraftforge.fml.network.simple.SimpleChannel.networkEventListener(SimpleChannel.java:64) ~[?:?]
at net.minecraftforge.fml.network.simple.SimpleChannel$$Lambda$1974/515186993.accept(Unknown Source) ~[?:?]
at net.minecraftforge.eventbus.EventBus.doCastFilter(EventBus.java:212) ~[eventbus-0.10.3-milestone.0.1+1a5fa31-service.jar:?]
at net.minecraftforge.eventbus.EventBus.lambda$addListener$11(EventBus.java:204) ~[eventbus-0.10.3-milestone.0.1+1a5fa31-service.jar:?]
at net.minecraftforge.eventbus.EventBus$$Lambda$1976/1749003390.invoke(Unknown Source) ~[?:?]
at net.minecraftforge.eventbus.EventBus.post(EventBus.java:258) ~[eventbus-0.10.3-milestone.0.1+1a5fa31-service.jar:?]
at net.minecraftforge.fml.network.NetworkInstance.dispatch(NetworkInstance.java:82) ~[?:?]
at net.minecraftforge.fml.network.NetworkHooks.lambda$onCustomPayload$0(NetworkHooks.java:67) ~[?:?]
at net.minecraftforge.fml.network.NetworkHooks$$Lambda$4597/1855467807.apply(Unknown Source) ~[?:?]
at java.util.Optional.map(Optional.java:215) ~[?:1.8.0_51]
at net.minecraftforge.fml.network.NetworkHooks.onCustomPayload(NetworkHooks.java:67) ~[?:?]
at net.minecraft.client.network.play.ClientPlayNetHandler.func_147240_a(ClientPlayNetHandler.java:1772) ~[?:?]
at net.minecraft.network.play.server.SCustomPayloadPlayPacket.func_148833_a(SCustomPayloadPlayPacket.java:55) ~[?:?]
at net.minecraft.network.play.server.SCustomPayloadPlayPacket.func_148833_a(SCustomPayloadPlayPacket.java:11) ~[?:?]
at net.minecraft.network.PacketThreadUtil.func_210405_a(SourceFile:15) ~[?:?]
at net.minecraft.network.PacketThreadUtil$$Lambda$4679/1897391336.run(Unknown Source) ~[?:?]
at net.minecraft.util.concurrent.ThreadTaskExecutor.func_213166_h(SourceFile:135) [?:?]
at net.minecraft.util.concurrent.RecursiveEventLoop.func_213166_h(SourceFile:23) [?:?]
at net.minecraft.util.concurrent.ThreadTaskExecutor.func_213168_p(SourceFile:114) [?:?]
at net.minecraft.util.concurrent.ThreadTaskExecutor.func_213160_bf(SourceFile:99) [?:?]
at net.minecraft.client.Minecraft.func_195542_b(Minecraft.java:856) [?:?]
at net.minecraft.client.Minecraft.func_99999_d(Minecraft.java:384) [?:?]
at net.minecraft.client.main.Main.main(SourceFile:154) [?:?]
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) ~[?:1.8.0_51]
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62) ~[?:1.8.0_51]
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) ~[?:1.8.0_51]
at java.lang.reflect.Method.invoke(Method.java:497) ~[?:1.8.0_51]
at net.minecraftforge.fml.loading.FMLClientLaunchProvider.lambda$launchService$0(FMLClientLaunchProvider.java:56) [forge-1.14.3-27.0.53.jar:27.0]
at net.minecraftforge.fml.loading.FMLClientLaunchProvider$$Lambda$337/973604791.call(Unknown Source) [forge-1.14.3-27.0.53.jar:27.0]
at cpw.mods.modlauncher.LaunchServiceHandlerDecorator.launch(LaunchServiceHandlerDecorator.java:37) [modlauncher-3.0.1.jar:?]
at cpw.mods.modlauncher.LaunchServiceHandler.launch(LaunchServiceHandler.java:50) [modlauncher-3.0.1.jar:?]
at cpw.mods.modlauncher.LaunchServiceHandler.launch(LaunchServiceHandler.java:68) [modlauncher-3.0.1.jar:?]
at cpw.mods.modlauncher.Launcher.run(Launcher.java:80) [modlauncher-3.0.1.jar:?]
at cpw.mods.modlauncher.Launcher.main(Launcher.java:65) [modlauncher-3.0.1.jar:?]
[15:45:10] [Client thread/INFO]: Received config from the server: {"minecraft:hide_infestations":true}
[15:45:10] [Client thread/INFO]: Loaded 972 advancements
[15:45:11] [Server thread/WARN]: Can't keep up! Is the server overloaded? Running 2207ms or 44 ticks behind
[15:45:12] [Client thread/WARN]: Unknown custom packed identifier: ender_compass:channel
[15:45:58] [Server thread/INFO]: Saving and pausing game...
[15:45:58] [Server thread/INFO]: Saving chunks for level '1.14.3'/minecraft:overworld
[15:46:15] [Server thread/INFO]: [CykaBlyatGopnik: Teleported CykaBlyatGopnik to 1514.5, 65.0, -4113.5]
[15:49:04] [Client thread/INFO]: [CHAT] Saved screenshot as 2019-07-16_15.49.04.png
The teleport command functions properly and there are no issues if I go short distances, but when I use it to go long distances, the aforementioned bug (permanent lag, I guess you could call it) occurs. If I teleport over a long distance, the area that I teleport to loads properly, but I have found that it loads only a few chunks and then stops (If I recall correctly, it loaded approximately the same number of chunks both times I tested it). If I go into the void, my player never returns to the world and I am stuck there in free-fall until I close the application (attempting to go to the main menu gets me stuck at a "Saving world" screen. I have also had that occur a few times randomly upon death in other worlds, such that respawning and going to the main menu does not work.)
Hopefully the log is sufficient, I assumed that anything that occurs in the bootup process of Minecraft that is logged is not relevant (I could be wrong of course, and if so I can provide the full log upon request.)