11:58:53 PM: ---------------------------------------------------------------------
  UNSUPPORTED BUILD IMAGE

  The build image for this site uses Ubuntu 16.04 Xenial Xerus, which is no longer supported.

  To enable builds for this site, select a later build image at the following link:
  https://app.netlify.com/sites/epic-yalow-39a3ea/settings/deploys#build-image-selection

  For more details, visit the build migration guide:
  https://answers.netlify.com/t/please-read-end-of-support-for-xenial-build-image-everything-you-need-to-know/68239
  ---------------------------------------------------------------------

どうやら、ビルドが OS のバージョンが古くて通らないようです。

エラー１の解決方法

これは Netlify の管理画面でポチポチすれば解決します。

アカウントホーム ⇨ サイトを選択 ⇨SiteSetting⇨
サイドメニューから「Build & Deploy」
Build image selection の EditSettings
Ubuntu Focal 20.04 (default)に変更

エラー内容２

11:05:05 AM: build-image version: d7b3813f01c06610bc1723ff1b22446513ee7941 (focal)
11:05:05 AM: build-image tag: v4.14.3
11:05:05 AM: buildbot version: 4bbbb4f3037b3dc1dcca89f1a4b61b3a106a845b
11:05:21 AM: Fetching cached dependencies
11:05:21 AM: Failed to fetch cache, continuing with build
11:05:21 AM: Starting to prepare the repo for build
11:05:21 AM: No cached dependencies found. Cloning fresh repo
11:05:21 AM: git clone https://github.com/username/blog
11:07:30 AM: Error cloning repository: https://github.com/username/blog
11:07:30 AM: Creating deploy upload records
11:07:30 AM: Failing build: Failed to prepare repo
11:07:41 AM: Failed during stage 'preparing repo': exit status 128
11:07:41 AM: Finished processing build request in 2m35.220824723s

どうやらキャッシュの fetch に失敗したようです。