vite-plugin-css-injected-by-jsはメンテナンスされていないため、通常のソースマップ生成に影響を与えるので、vite-plugin-lib-injected-cssを使用してください

plugin/kintone-addins/package.json

@@ -8,12 +8,10 @@
     "watch": "vite build --watch --mode dev",
     "server": "vite dev --mode dev",
     "ngrok": "ngrok http 4173",
-
     "build": "run-s b:production copy:windows",
     "build:dev": "run-s b:dev copy:windows",
     "build:linux": "run-s b:production copy:linux",
     "build:linux-dev": "run-s b:dev copy:linux",
-
     "b:production": "vite build --mode production",
     "b:dev": "vite build --mode dev",
     "copy:windows": "xcopy dist\\*.js ..\\..\\backend\\Temp\\ /E /I /Y",
@@ -26,10 +24,10 @@
     "sass": "^1.69.5",
     "typescript": "^5.0.2",
     "vite": "^4.4.5",
-    "vite-plugin-checker": "^0.6.4"
+    "vite-plugin-checker": "^0.6.4",
+    "vite-plugin-lib-inject-css": "^2.1.1"
   },
   "dependencies": {
-    "jquery": "^3.7.1",
-    "vite-plugin-css-injected-by-js": "^3.5.1"
+    "jquery": "^3.7.1"
   }
 }

plugin/kintone-addins/vite.config.js

@@ -1,7 +1,7 @@
 // vite.config.js
 import { defineConfig, loadEnv } from "vite";
-import cssInjectedByJsPlugin from "vite-plugin-css-injected-by-js";
 import checker from "vite-plugin-checker";
+import { libInjectCss } from 'vite-plugin-lib-inject-css';
 
 export default ({ mode }) => {
   process.env = { ...process.env, ...loadEnv(mode, process.cwd()) };
@@ -11,7 +11,7 @@ export default ({ mode }) => {
       checker({
         typescript: true,
       }),
-      cssInjectedByJsPlugin(),
+      libInjectCss(),
     ],
     build: {
       cssCodeSplit: false,