diff --git a/php/class-delivery.php b/php/class-delivery.php
index 1d920518f..a4eaa7452 100644
--- a/php/class-delivery.php
+++ b/php/class-delivery.php
@@ -541,6 +541,8 @@ public function unsync_size_relationship( $attachment_id ) {
 	 */
 	public function get_sized( $attachment_id ) {
 		static $sizes = array(), $registered_sizes;
+
+		$attachment_id = (int) $attachment_id;
 		if ( ! $registered_sizes ) {
 			$registered_sizes = wp_get_registered_image_subsizes();
 		}
@@ -920,13 +922,17 @@ public function find_attachment_size_urls() {
 			$search
 		);
 
+		// Cache for the current request only. Across requests, failed deliveries or syncs need to be retried,
+		// and the contextualized post IDs can differ (e.g. per WPML language).
+		static $cache = array();
+
 		$key       = md5( $sql );
-		$cached    = wp_cache_get( $key );
+		$cached    = isset( $cache[ $key ] ) ? $cache[ $key ] : false;
 		$auto_sync = $this->sync->is_auto_sync_enabled();
 
 		if ( false === $cached ) {
 			$cached  = array();
-			$results = $wpdb->get_results( $sql ); // phpcs:ignore WordPress.DB.DirectDatabaseQuery.DirectQuery, WordPress.DB.PreparedSQL.NotPrepared
+			$results = $wpdb->get_results( $sql ); // phpcs:ignore WordPress.DB.DirectDatabaseQuery.DirectQuery, WordPress.DB.DirectDatabaseQuery.NoCaching, WordPress.DB.PreparedSQL.NotPrepared
 
 			if ( $results ) {
 				foreach ( $results as $result ) {
@@ -942,7 +948,8 @@ public function find_attachment_size_urls() {
 					 */
 					$post_id = apply_filters( 'cloudinary_contextualized_post_id', $result->post_id );
 
-					if ( ! $this->is_deliverable( $post_id ) ) {
+					// The contextualized post can be missing, e.g. WPML returns null for an attachment without a translation.
+					if ( empty( $post_id ) || ! $this->is_deliverable( $post_id ) ) {
 						continue;
 					}
 					// If we are here, it means that an attachment in the media library doesn't have a delivery for the url.
@@ -953,11 +960,13 @@ public function find_attachment_size_urls() {
 						$this->sync->add_to_sync( $post_id );
 					}
 					$size           = $this->get_sized( $post_id );
-					$key            = ! empty( $size['sized_url'] ) ? $size['sized_url'] : wp_get_attachment_url( $post_id );
-					$cached[ $key ] = (int) $post_id;
+					$attachment_url = ! empty( $size['sized_url'] ) ? $size['sized_url'] : wp_get_attachment_url( $post_id );
+					if ( $attachment_url ) {
+						$cached[ $attachment_url ] = (int) $post_id;
+					}
 				}
 			}
-			wp_cache_add( $key, $cached );
+			$cache[ $key ] = $cached;
 		}
 
 		$this->known   = array_merge( $this->known, $cached );
diff --git a/php/class-media.php b/php/class-media.php
index 9948db77b..65f6daf57 100644
--- a/php/class-media.php
+++ b/php/class-media.php
@@ -3180,7 +3180,7 @@ public function get_cloudinary_version( $attachment_id ) {
 			$attachment = get_post( $attachment_id );
 
 			if ( ! empty( $attachment ) && Assets::POST_TYPE_SLUG === $attachment->post_type && ! empty( $attachment->post_parent ) ) {
-				$version = (int) preg_replace( '/\D/', '', $this->get_post_meta( (int) $attachment->post_parent, Sync::META_KEYS['version'], true ) );
+				$version = (int) preg_replace( '/\D/', '', $this->get_post_meta( (int) $attachment->post_parent, Sync::META_KEYS['version'], true, '' ) );
 			}
 		}
 
diff --git a/php/class-string-replace.php b/php/class-string-replace.php
index 905fa9a27..fe13b160d 100644
--- a/php/class-string-replace.php
+++ b/php/class-string-replace.php
@@ -164,8 +164,31 @@ public function init() {
 	 * Stop the buffer capture and set the output callback.
 	 */
 	public function start_capture() {
-		ob_start( array( $this, 'replace_strings' ) );
-		ob_start( array( $this, 'replace_strings' ) ); // Second call to catch early buffer flushing.
+		ob_start( array( $this, 'output_handler' ) );
+		ob_start( array( $this, 'output_handler' ) ); // Second call to catch early buffer flushing.
+	}
+
+	/**
+	 * Output buffer callback to replace strings in the captured buffer.
+	 *
+	 * Output produced within an output handler is discarded, and doing so is deprecated as of PHP 8.4.
+	 * Errors displayed while replacing (e.g. notices raised by hooked callbacks) would count as such output,
+	 * so display is disabled for the duration of the handler. Errors are still logged as usual.
+	 * This doesn't cover callbacks that echo output directly, which still trigger the deprecation.
+	 *
+	 * @param string $buffer The captured buffer.
+	 * @param int    $phase  The output handler phase bitmask.
+	 *
+	 * @return string
+	 */
+	public function output_handler( $buffer, $phase ) {
+		$display_errors = ini_set( 'display_errors', '0' ); // phpcs:ignore WordPress.PHP.IniSet.display_errors_Disallowed
+		$buffer         = $this->replace_strings( $buffer, $phase );
+		if ( false !== $display_errors ) {
+			ini_set( 'display_errors', $display_errors ); // phpcs:ignore WordPress.PHP.IniSet.display_errors_Disallowed
+		}
+
+		return $buffer;
 	}
 
 	/**
@@ -285,7 +308,7 @@ protected function prime_replacements( $content, $context = 'view' ) {
 	 * Replace string in HTML.
 	 *
 	 * @param string|array $content The HTML.
-	 * @param string       $context The context to use.
+	 * @param string|int   $context The context to use, or the output handler phase when capturing a buffer.
 	 *
 	 * @return string
 	 */
diff --git a/php/relate/class-relationship.php b/php/relate/class-relationship.php
index bedeef302..172e4ac14 100644
--- a/php/relate/class-relationship.php
+++ b/php/relate/class-relationship.php
@@ -270,11 +270,12 @@ public function delete_cache() {
 	public static function get_relationship( $post_id ) {
 
 		static $cache = array();
-		if ( ! isset( $cache[ $post_id ] ) ) {
-			$cache[ $post_id ] = new self( $post_id );
+		$key          = (int) $post_id;
+		if ( ! isset( $cache[ $key ] ) ) {
+			$cache[ $key ] = new self( $post_id );
 		}
 
-		return $cache[ $post_id ];
+		return $cache[ $key ];
 	}
 
 	/**
diff --git a/php/ui/class-component.php b/php/ui/class-component.php
index 71b0396e1..bea5e9dac 100644
--- a/php/ui/class-component.php
+++ b/php/ui/class-component.php
@@ -618,7 +618,7 @@ public static function build_tag( $element, $attributes = array(), $state = 'ope
 	/**
 	 * Get a build part to construct.
 	 *
-	 * @param string|null $part The part name.
+	 * @param string $part The part name.
 	 *
 	 * @return array
 	 */
diff --git a/php/ui/component/class-opt-level.php b/php/ui/component/class-opt-level.php
index 5ff1eb178..8d32e5c0d 100644
--- a/php/ui/component/class-opt-level.php
+++ b/php/ui/component/class-opt-level.php
@@ -119,7 +119,7 @@ protected function get_setting_line( $slug ) {
 	protected function get_badge( $status = 'active' ) {
 		$badge                          = $this->get_part( 'span' );
 		$badge['attributes']['class'][] = "cld-optimisation-item-{$status}";
-		$text                           = $this->get_part( null );
+		$text                           = $this->get_part( '' );
 		if ( 'active' === $status ) {
 			$text['content']           = __( 'Activated', 'cloudinary' );
 			$icon                      = $this->dashicon( $this->get_part( 'span' ) );