Record the environment first
Write down Minecraft version, loader and loader version, Quark version, Zeta version and the list of recently changed mods. This turns an unclear crash into a reproducible test case.
If you changed several mods at once, restore the last known working set and reapply changes gradually.
Read the log before deleting files
The first meaningful error often points to a missing dependency, incompatible version or class-loading failure. The final crash message may be generic and less useful.
Keep logs private when they include usernames or local file paths you do not want to share publicly.
Test a minimal profile
Create a fresh profile with the same Minecraft and loader versions. Add only Quark and its required dependency. If the issue disappears, another mod or configuration in the original pack is involved.
Add other mods back in groups, then narrow the group until you find the conflict.
Missing feature or recipe
Confirm the relevant Quark module is enabled and that the feature exists in your release. Recipe viewers reflect the running instance and are often more reliable than an old tutorial.
For servers, compare client and server configuration because the server may control the effective behavior.
Update without losing your fallback
Keep the previous working mod files and a world backup until the new setup has passed several launches. Do not overwrite your only copy during troubleshooting.