all tests passing

packages/svelte/src/compiler/phases/3-transform/client/visitors/template.js

@@ -943,6 +943,7 @@ function serialize_inline_component(node, component_name, context) {
 		fn = (node_id) => {
 			return b.call(
 				'$.component',
+				node_id,
 				b.thunk(/** @type {import('estree').Expression} */ (context.visit(node.expression))),
 				b.arrow(
 					[b.id(component_name)],
@@ -1687,12 +1688,24 @@ export const template_visitors = {
 					flags |= TEMPLATE_USE_IMPORT_NODE;
 				}
 
-				if (trimmed[0].type === 'Component' || trimmed[0].type === 'SlotElement') {
+				var first = trimmed[0];
+
+				if (first.type === 'SlotElement') {
 					flags |= TEMPLATE_UNSET_START;
 				}
 
-				if (trimmed[0].type === 'RenderTag') {
+				if (first.type === 'Component') {
-					const callee = unwrap_optional(trimmed[0].expression).callee;
+					// if it's not a `$.component`, mark as unset
+					const binding = context.state.scope.get(
+						first.name.includes('.') ? first.name.slice(0, first.name.indexOf('.')) : first.name
+					);
+					if (binding === null || binding.kind === 'normal') {
+						flags |= TEMPLATE_UNSET_START;
+					}
+				}
+
+				if (first.type === 'RenderTag') {
+					const callee = unwrap_optional(first.expression).callee;
 					const is_reactive =
 						callee.type !== 'Identifier' || context.state.scope.get(callee.name)?.kind !== 'normal';
 
@@ -2998,6 +3011,7 @@ export const template_visitors = {
 				b.stmt(
 					b.call(
 						'$.component',
+						context.state.node,
 						// TODO use untrack here to not update when binding changes?
 						// Would align with Svelte 4 behavior, but it's arguably nicer/expected to update this
 						b.thunk(

packages/svelte/src/internal/client/dom/blocks/svelte-component.js

@@ -9,14 +9,14 @@ import { block, branch, pause_effect } from '../../reactivity/effects.js';
  * @param {(component: C) => import('#client').Dom | void} render_fn
  * @returns {void}
  */
-export function component(get_component, render_fn) {
+export function component(anchor, get_component, render_fn) {
 	/** @type {C} */
 	let component;
 
 	/** @type {import('#client').Effect | null} */
 	let effect;
 
-	block(null, 0, () => {
+	block(anchor, 0, () => {
 		if (component === (component = get_component())) return;
 
 		if (effect) {

packages/svelte/src/internal/client/dom/template.js

@@ -71,6 +71,10 @@ export function template(content, flags) {
 
 		assign_nodes(start, end);
 
+		if (unset) {
+			current_effect.nodes.anchor = clone.firstChild;
+		}
+
 		return clone;
 	};
 }
@@ -258,11 +262,16 @@ export function comment(flags = 0) {
 		return hydrate_start;
 	}
 
+	var unset = (flags & TEMPLATE_UNSET_START) !== 0;
 	var frag = document.createDocumentFragment();
 	var anchor = empty();
 	frag.append(anchor);
 
-	assign_nodes((flags & TEMPLATE_UNSET_START) !== 0 ? undefined : null, anchor);
+	assign_nodes(unset ? undefined : null, anchor);
+
+	if (unset) {
+		current_effect.nodes.anchor = anchor;
+	}
 
 	return frag;
 }

packages/svelte/src/internal/client/reactivity/effects.js

@@ -385,7 +385,11 @@ export function destroy_effect(effect, remove_dom = true) {
  */
 export function get_first_node(effect) {
 	if (effect.nodes !== null) {
-		if (effect.nodes.start != null) {
+		if (effect.nodes.start === undefined) {
+			return effect.nodes.anchor;
+		}
+
+		if (effect.nodes.start !== null) {
 			return effect.nodes.start;
 		}
 	}