Troubleshoot startup, missing cities, generation issues and mismatched versions. This guide focuses on a repeatable setup process rather than assuming every launcher, modpack or server uses the same files.
Startup crash
Start by comparing the game version, Java version, Forge version and Lost Cities build. The first relevant error in the log is usually more useful than the final generic crash message.
Cities are missing
Verify the profile or dimension setup and travel into chunks that have never been generated. Old terrain will not retroactively rebuild itself just because settings changed.
Generation looks corrupted
Disable newly added world-generation addons and test in a fresh world. If the base mod works, reintroduce custom content one component at a time.
Report reproducible details
When seeking support, include exact versions, the selected profile, a short mod list and the smallest set of steps that reproduces the issue.