Instead of overwriting the minify_exclude value, append your css file to it.

Plugin/View/ExcludeCssFromMinification.php

@@ -0,0 +1,65 @@
+<?php
+/**
+ * NOTICE OF LICENSE
+ *
+ * This source file is subject to the Open Software License (OSL 3.0)
+ * that is available through the world-wide-web at this URL:
+ * http://opensource.org/licenses/osl-3.0.php
+ */
+
+namespace Magenerds\PageDesigner\Plugin\View;
+
+use Magento\Framework\View\Asset\Minification;
+
+/**
+ * Class ExcludeCssFromMinification
+ *
+ * @package     Magenerds\PageDesigner\Plugin\View
+ * @file        ExcludeCssFromMinification.php
+ */
+class ExcludeCssFromMinification
+{
+    /**
+     * Adds css file to the minify_exclude config setting to avoid a bug with minification of this css file
+     * Only occurs with tubalmartin/cssmin < v2.4.8-p7
+     *
+     * Ref:
+     * - https://github.com/magento/magento2/issues/8552
+     * - https://github.com/magento/magento2/pull/9027
+     * - https://github.com/tubalmartin/YUI-CSS-compressor-PHP-port/commit/59e5e8b0b8225244aea90da3cd5f81b1ba575da2#diff-80f11f7052c350cef68c3041a5479789R588
+     *
+     * @param Minification $subject
+     * @param callable $proceed
+     * @param string $contentType
+     * @return string[]
+     */
+    public function aroundGetExcludes(Minification $subject, callable $proceed, $contentType)
+    {
+        $result = $proceed($contentType);
+
+        if ($contentType !== 'css' || !$this->isCssminLibraryOlderThanVersion3()) {
+            return $result;
+        }
+
+        $result[] = '/Magenerds_PageDesigner/css/pd-ui.css';
+
+        return $result;
+    }
+
+    /**
+     * Checks if the current version of tubalmartin/cssmin can cause problems with minifying
+     * Strictly speaking, not all versions 2.x.x of the library caused issues (since it got fixed in v2.4.8-p7),
+     * but here we check to see if version 2 is being used, where the class was called 'CSSmin' and existed in the global namespace,
+     * from version 3 on out, the class name was changed and put in a namespace: 'tubalmartin\CssMin\Minifier'
+     * So if we detect version 2 of the library, we assume it is broken
+     *
+     * Ref:
+     * - https://github.com/tubalmartin/YUI-CSS-compressor-PHP-port/compare/v2.4.8-p10...v3.0.0#diff-411bfa1ca68f3e86ffb0276bcffd838dL22
+     *
+     * @return bool
+     */
+    private function isCssminLibraryOlderThanVersion3()
+    {
+        return class_exists(\CSSmin::class);
+    }
+}

etc/config.xml

@@ -11,14 +11,6 @@
 <config xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:noNamespaceSchemaLocation="urn:magento:module:Magento_Store:etc/config.xsd">
     <default>
-        <dev>
-            <!-- temporary solution until https://github.com/magento/magento2/issues/8552 is fixed-->
-            <css>
-                <minify_exclude>
-                    /Magenerds_PageDesigner/css/pd-ui.css
-                </minify_exclude>
-            </css>
-        </dev>
         <pagedesigner>
             <general>
                 <css_classes_column>pd-highlight</css_classes_column>

etc/di.xml

@@ -46,4 +46,10 @@
         <plugin name="Magenerds_PageDesigner::widgetDecodeBackend"
                 type="Magenerds\PageDesigner\Plugin\Block\WidgetOptionsPlugin"/>
     </type>
+
+    <!-- needed for tubalmartin/cssmin < v2.4.8-p7 -->
+    <type name="Magento\Framework\View\Asset\Minification">
+        <plugin name="Magenerds_PageDesigner::excludeCssFromMinification"
+                type="Magenerds\PageDesigner\Plugin\View\ExcludeCssFromMinification"/>
+    </type>
 </config>