Category Order could not understand your category HTML. Please do the following:

• Disable all plugins except for category order to see if some other plugin is causing the problem. If the problem goes away, re-enable each plugin until you find the incompatible one.
• Try switching to a different theme, like the WordPress default theme.

Once you have tried the above steps, email david@coppit.org with the results of these debugging steps. Also include the following information:

Original HTML:
<li class="cat-item cat-item-3"><a href="https://nakae-mitsuki.net/information/?cat=3" >お知らせ</a>
</li>
<li class="cat-item cat-item-1"><a href="https://nakae-mitsuki.net/information/?cat=1" >その他</a>
</li>
<li class="cat-item cat-item-6"><a href="https://nakae-mitsuki.net/information/?cat=6" >イベント情報</a>
</li>
<li class="cat-item cat-item-5"><a href="https://nakae-mitsuki.net/information/?cat=5" >ライブ情報</a>
</li>
<li class="cat-item cat-item-7"><a href="https://nakae-mitsuki.net/information/?cat=7" >作品情報</a>
</li>
<li class="cat-item cat-item-4"><a href="https://nakae-mitsuki.net/information/?cat=4" >参加・出演情報</a>
</li>

Processed HTML:
<li class="cat-item cat-item-3"><a href="https://nakae-mitsuki.net/information/?cat=3" >お知らせ</a>
</li>
<li class="cat-item cat-item-1"><a href="https://nakae-mitsuki.net/information/?cat=1" >その他</a>
</li>
<li class="cat-item cat-item-6"><a href="https://nakae-mitsuki.net/information/?cat=6" >イベント情報</a>
</li>
<li class="cat-item cat-item-5"><a href="https://nakae-mitsuki.net/information/?cat=5" >ライブ情報</a>
</li>
<li class="cat-item cat-item-7"><a href="https://nakae-mitsuki.net/information/?cat=7" >作品情報</a>
</li>
<li class="cat-item cat-item-4"><a href="https://nakae-mitsuki.net/information/?cat=4" >参加・出演情報</a>
</li>

Category pattern:
/http\:\/\/nakae-mitsuki\.net\/information\/\?cat\=(\d+)/

Items:
Array
(
    [0] => <li class="cat-item cat-item-3"><a href="https://nakae-mitsuki.net/information/?cat=3" >お知らせ</a> </li>
    [1] => <li class="cat-item cat-item-1"><a href="https://nakae-mitsuki.net/information/?cat=1" >その他</a> </li>
    [2] => <li class="cat-item cat-item-6"><a href="https://nakae-mitsuki.net/information/?cat=6" >イベント情報</a> </li>
    [3] => <li class="cat-item cat-item-5"><a href="https://nakae-mitsuki.net/information/?cat=5" >ライブ情報</a> </li>
    [4] => <li class="cat-item cat-item-7"><a href="https://nakae-mitsuki.net/information/?cat=7" >作品情報</a> </li>
    [5] => <li class="cat-item cat-item-4"><a href="https://nakae-mitsuki.net/information/?cat=4" >参加・出演情報</a> </li>
)