Why the log don't tell me where is the cross reference mentioning this vanilla item?
Could not resolve cross-reference: No Verse.ThingDef named Turret_Sniper found to give to MapGeneratorBlueprints.MapGenerator.ThingData MapGeneratorBlueprints.MapGenerator.ThingData
Verse.Log:Error(String, Boolean)
Verse.WantedRefForObject:TryResolve(FailMode)
Verse.DirectXmlCrossRefLoader:ResolveAllWantedCrossReferences(FailMode)
Verse.PlayDataLoader:DoPlayLoad()
It is telling you?
Some mod (maybe core, probably not) needs it for making a map from blueprints. Maybe the ruins mod? Maybe the faction base mod?
I have no idea why your Turret_Sniper is missing. Perhaps a different mod replaced the turrets with their own copy, but the blueprint doesn't know this?
Hope that helps.
Yes, somehow, I'll dig deeper (famous last words)
Searching your Mod folder (and/or steam workshop folder) for any xml files that contain "Turret_Sniper" is probably a helpful step.