fix: better message

src/runtime/internal/dev.ts

@@ -157,7 +157,9 @@ export class SvelteComponentDev extends SvelteComponent {
 		}
 
 		if (!options.target && !current_component) {
-			throw new Error("Multiple Svelte instances detected. Please ensure only one instance exists, or set the 'target' option");
+			throw new Error(
+				"Multiple Svelte instances detected. This can happen if you use Svelte components which are precompiled to JavaScript. " +
+					"Ensure to use the raw Svelte version of these components, or set the 'target' option instead");
 		}
 
 		super();