[04Sep2023 21:20:53.410] [main/INFO] [cpw.mods.modlauncher.Launcher/MODLAUNCHER]: ModLauncher running: args [--username, ReshyShira, --version, forge-43.2.21, --gameDir, E:\Personal\Archive\Games\Twitch MC\Instances\1.19.2 DS, --assetsDir, E:\Personal\Archive\Games\Twitch MC\Install\assets, --assetIndex, 1.19, --uuid, f88d39c334994aa8bdb42ceaa95cee0e, --accessToken, ????????, --clientId, YjMwMGJiY2ItNzVlZi00MmY2LWJhMTgtOTA3NWRjZjUxMjg2, --xuid, 2535471593108702, --userType, msa, --versionType, release, --width, 1024, --height, 768, --launchTarget, forgeclient, --fml.forgeVersion, 43.2.21, --fml.mcVersion, 1.19.2, --fml.forgeGroup, net.minecraftforge, --fml.mcpVersion, 20220805.130853]
[04Sep2023 21:20:53.417] [main/INFO] [cpw.mods.modlauncher.Launcher/MODLAUNCHER]: ModLauncher 10.0.8+10.0.8+main.0ef7e830 starting: java version 17.0.3 by Microsoft; OS Windows 10 arch amd64 version 10.0
[04Sep2023 21:20:56.450] [main/INFO] [mixin/]: SpongePowered MIXIN Subsystem Version=0.8.5 Source=union:/E:/Personal/Archive/Games/Twitch%20MC/Install/libraries/org/spongepowered/mixin/0.8.5/mixin-0.8.5.jar%2397!/ Service=ModLauncher Env=CLIENT
[04Sep2023 21:20:56.540] [main/INFO] [io.dogboy.serializationisbad.core.SerializationIsBad/]: Initializing SerializationIsBad, implementation type: modlauncher
[04Sep2023 21:21:40.815] [main/ERROR] [io.dogboy.serializationisbad.core.SerializationIsBad/]: Failed to load remote config file
java.io.IOException: Invalid response code: 503
at io.dogboy.serializationisbad.core.SerializationIsBad.readRemoteConfig(SerializationIsBad.java:121) ~[?:?]
at io.dogboy.serializationisbad.core.SerializationIsBad.readConfig(SerializationIsBad.java:101) ~[?:?]
at io.dogboy.serializationisbad.core.SerializationIsBad.(SerializationIsBad.java:61) ~[?:?]
at io.dogboy.serializationisbad.core.SerializationIsBad.init(SerializationIsBad.java:43) ~[?:?]
at io.dogboy.serializationisbad.modlauncher.SerializationIsBadTransformationService.initialize(SerializationIsBadTransformationService.java:36) ~[?:?]
at cpw.mods.modlauncher.TransformationServiceDecorator.onInitialize(TransformationServiceDecorator.java:68) ~[modlauncher-10.0.8.jar%2388!/:?]
at cpw.mods.modlauncher.TransformationServicesHandler.lambda$initialiseTransformationServices$7(TransformationServicesHandler.java:92) ~[modlauncher-10.0.8.jar%2388!/:?]
at java.util.HashMap$Values.forEach(HashMap.java:1065) [?:?]
at cpw.mods.modlauncher.TransformationServicesHandler.initialiseTransformationServices(TransformationServicesHandler.java:92) [modlauncher-10.0.8.jar%2388!/:?]
at cpw.mods.modlauncher.TransformationServicesHandler.initializeTransformationServices(TransformationServicesHandler.java:51) [modlauncher-10.0.8.jar%2388!/:?]
at cpw.mods.modlauncher.Launcher.run(Launcher.java:87) [modlauncher-10.0.8.jar%2388!/:?]
at cpw.mods.modlauncher.Launcher.main(Launcher.java:77) [modlauncher-10.0.8.jar%2388!/:?]
at cpw.mods.modlauncher.BootstrapLaunchConsumer.accept(BootstrapLaunchConsumer.java:26) [modlauncher-10.0.8.jar%2388!/:?]
at cpw.mods.modlauncher.BootstrapLaunchConsumer.accept(BootstrapLaunchConsumer.java:23) [modlauncher-10.0.8.jar%2388!/:?]
at cpw.mods.bootstraplauncher.BootstrapLauncher.main(BootstrapLauncher.java:141) [bootstraplauncher-1.1.2.jar:?]
[04Sep2023 21:21:40.821] [main/INFO] [io.dogboy.serializationisbad.core.SerializationIsBad/]: Using local config file as a fallback

[04Sep2023 21:21:40.815] [main/ERROR] [io.dogboy.serializationisbad.core.SerializationIsBad/]: Failed to load remote config file java.io.IOException: Invalid response code: 503

It looks like SiB was unable to load the remote config file from Github during the game startup (probably because of temporary issues on Githubs side). You could try again after a few minutes which should solve the issue.

In version 1.5 this issue should be resolved due to local caching of the remote config file in case of temporary failure to read it from Github.

Fixed in version 1.5