ServiceWorkerで警告が表示されてしまいます。

サイト読み込み時に下記の警告が表示されてしまうのですが、原因がわかりません

Console
1The resource ((manifest,jsonのURL)) was preloaded using link preload but not used within a few seconds from the window's load event. Please make sure it wasn't preloaded for nothing.
2The resource ((画像のURL)) was preloaded using link preload but not used within a few seconds from the window's load event. Please make sure it wasn't preloaded for nothing.
3The resource ((画像のURL)) was preloaded using link preload but not used within a few seconds from the window's load event. Please make sure it wasn't preloaded for nothing.
4The resource ((画像のURL)) was preloaded using link preload but not used within a few seconds from the window's load event. Please make sure it wasn't preloaded for nothing.
51 The resource ((画像のURL)) was preloaded using link preload but not used within a few seconds from the window's load event. Please make sure it wasn't preloaded for nothing.

Json
1{
2    "name": "((自サイトの名前))",
3    "icons": [
4        {
5            "src": "android-chrome-192x192.png",
6            "sizes": "192x192",
7            "type": "image/png"
8        },
9        {
10            "src": "android-chrome-512x512.png",
11            "sizes": "512x512",
12            "type": "image/png"
13        }
14    ],
15    "theme_color": "#ffffff",
16    "start_url": "((自サイトのURL))",
17    "display": "standalone"
18}