diff --git a/public/src/modules/api.js b/public/src/modules/api.js
index 55abd1ad36..7c1038fbde 100644
--- a/public/src/modules/api.js
+++ b/public/src/modules/api.js
@@ -79,7 +79,11 @@ async function xhr(options) {
 
 	if (!res.ok) {
 		if (response) {
-			throw new Error(isJSON ? response.status.message : response);
+			const jsonError = isJSON && (response.status?.message || response.error || '');
+			throw new Error(isJSON && jsonError ?
+				jsonError :
+				response
+			);
 		}
 		throw new Error(res.statusText);
 	}
diff --git a/src/categories/create.js b/src/categories/create.js
index 92f63f27e6..fa49468834 100644
--- a/src/categories/create.js
+++ b/src/categories/create.js
@@ -101,7 +101,7 @@ module.exports = function (Categories) {
 		await privileges.categories.give(result.guestPrivileges, category.cid, ['guests', 'spiders']);
 
 		cache.del('categories:cid');
-		await clearParentCategoryCache(parentCid);
+		await Categories.clearParentCategoryCache(parentCid);
 
 		if (data.cloneFromCid && parseInt(data.cloneFromCid, 10)) {
 			category = await Categories.copySettingsFrom(data.cloneFromCid, category.cid, !data.parentCid);
@@ -115,8 +115,8 @@ module.exports = function (Categories) {
 		return category;
 	};
 
-	async function clearParentCategoryCache(parentCid) {
-		while (parseInt(parentCid, 10) >= 0) {
+	Categories.clearParentCategoryCache = async function (parentCid) {
+		while (parentCid || parseInt(parentCid, 10) === 0) {
 			cache.del([
 				`cid:${parentCid}:children`,
 				`cid:${parentCid}:children:all`,
@@ -129,7 +129,7 @@ module.exports = function (Categories) {
 			// eslint-disable-next-line no-await-in-loop
 			parentCid = await Categories.getCategoryField(parentCid, 'parentCid');
 		}
-	}
+	};
 
 	async function duplicateCategoriesChildren(parentCid, cid, uid) {
 		let children = await Categories.getChildren([cid], uid);
@@ -188,17 +188,13 @@ module.exports = function (Categories) {
 			throw new Error('[[error:invalid-cid]]');
 		}
 
-		const oldParent = parseInt(destination.parentCid, 10) || 0;
-		const newParent = parseInt(source.parentCid, 10) || 0;
-		if (copyParent && newParent !== parseInt(toCid, 10)) {
+		const oldParent = String(destination.parentCid || 0);
+		const newParent = String(source.parentCid || 0);
+		if (copyParent && newParent !== String(toCid)) {
 			await db.sortedSetRemove(`cid:${oldParent}:children`, toCid);
 			await db.sortedSetAdd(`cid:${newParent}:children`, source.order, toCid);
-			cache.del([
-				`cid:${oldParent}:children`,
-				`cid:${oldParent}:children:all`,
-				`cid:${newParent}:children`,
-				`cid:${newParent}:children:all`,
-			]);
+			await Categories.clearParentCategoryCache(oldParent);
+			await Categories.clearParentCategoryCache(newParent);
 		}
 
 		destination.description = source.description;
diff --git a/src/categories/delete.js b/src/categories/delete.js
index 3074cf3f55..5f96e32676 100644
--- a/src/categories/delete.js
+++ b/src/categories/delete.js
@@ -79,12 +79,13 @@ module.exports = function (Categories) {
 		cache.del([
 			'categories:cid',
 			'cid:0:children',
-			`cid:${parentCid}:children`,
-			`cid:${parentCid}:children:all`,
-			`cid:${cid}:children`,
-			`cid:${cid}:children:all`,
+			'cid:0:children:all',
 			`cid:${cid}:tag:whitelist`,
 		]);
+		await Promise.all([
+			Categories.clearParentCategoryCache(parentCid),
+			Categories.clearParentCategoryCache(cid),
+		]);
 	}
 
 	async function deleteTags(cid) {
diff --git a/src/categories/update.js b/src/categories/update.js
index ff4d6e4d11..0579019e2f 100644
--- a/src/categories/update.js
+++ b/src/categories/update.js
@@ -85,12 +85,9 @@ module.exports = function (Categories) {
 			db.sortedSetAdd(`cid:${newParent}:children`, categoryData.order, cid),
 			db.setObjectField(`${utils.isNumber(cid) ? 'category' : 'categoryRemote'}:${cid}`, 'parentCid', newParent),
 		]);
-
-		cache.del([
-			`cid:${oldParent}:children`,
-			`cid:${newParent}:children`,
-			`cid:${oldParent}:children:all`,
-			`cid:${newParent}:children:all`,
+		await Promise.all([
+			Categories.clearParentCategoryCache(oldParent),
+			Categories.clearParentCategoryCache(newParent),
 		]);
 	}
 
@@ -134,11 +131,9 @@ module.exports = function (Categories) {
 		await db.setObjectBulk(
 			childrenCids.map((cid, index) => [`${utils.isNumber(cid) ? 'category' : 'categoryRemote'}:${cid}`, { order: index + 1 }])
 		);
-
+		await Categories.clearParentCategoryCache(parentCid);
 		cache.del([
 			'categories:cid',
-			`cid:${parentCid}:children`,
-			`cid:${parentCid}:children:all`,
 		]);
 	}
 
diff --git a/src/controllers/admin/categories.js b/src/controllers/admin/categories.js
index 5e503b1964..54c9b276f6 100644
--- a/src/controllers/admin/categories.js
+++ b/src/controllers/admin/categories.js
@@ -202,13 +202,14 @@ categoriesController.addRemote = async function (req, res) {
 		return res.sendStatus(404);
 	}
 
-	const score = await db.sortedSetCard('cid:0:children');
-	const order = score + 1; // order is 1-based lol
+	const lastItem = await db.getSortedSetRevRangeWithScores('cid:0:children', 0, 0);
+	const order = lastItem.length ? lastItem[0].score + 1 : 1;
 	await Promise.all([
 		db.sortedSetAdd('cid:0:children', order, id),
 		categories.setCategoryField(id, 'order', order),
 	]);
 	cache.del('cid:0:children');
+	cache.del('cid:0:children:all');
 
 	res.sendStatus(200);
 };
@@ -231,7 +232,7 @@ categoriesController.removeRemote = async function (req, res) {
 
 	const parentCid = await categories.getCategoryField(req.params.cid, 'parentCid');
 	await db.sortedSetRemove(`cid:${parentCid || 0}:children`, req.params.cid);
-	cache.del(`cid:${parentCid || 0}:children`);
-
+	await categories.clearParentCategoryCache(parentCid || 0);
+	await categories.setCategoryField(req.params.cid, 'parentCid', 0);
 	res.sendStatus(200);
 };