django UTF-8ファイルがUnicodeDecodeErrorと表示される

djangoでwebアプリを作成しています。
base.htmlをutf-8 BOM無しで保存しているのですが、
Unicode Decode Errorが表示されてしまいます。

error
1UnicodeDecodeError at /accountapp/
2'utf-8' codec can't decode byte 0x83 in position 17: invalid start byte
3Request Method:	POST
4Request URL:	
5Django Version:	2.2
6Exception Type:	UnicodeDecodeError
7Exception Value:	
8'utf-8' codec can't decode byte 0x83 in position 17: invalid start byte
9
10Unicode error hint
11The string that could not be encoded/decoded was: bel="�y�[�W
12
13Error during template rendering
14In template C:\virtualenv\manager\accounts\templates\base.html, error at line 0
15
16utf-8
171	{% load staticfiles %}
182	<!DOCTYPE html>
193	<html>
204	<head>
215	<meta charset="UTF-8">
226	<meta name="viewport" content="width=device-width, initial-scale=1">
237	    <link href="https://fonts.googleapis.com/css?family=Open+Sans" rel="stylesheet">
248	    <link href="{% static 'css/sb-admin-2.css' %}" rel="stylesheet">
259	    <link href="{% static 'manager/css/structure.css' %}" rel="stylesheet" type="text/css">
2610	    <title>{% if request.path != '/' %}{% block title %}{% endblock %} | {% endif %}Blog App with Auth | Django2 Tutorial</title>

base.html
1{% load staticfiles %}
2<!DOCTYPE html>
3<html>
4<head>
5<meta charset="UTF-8">
6<meta name="viewport" content="width=device-width, initial-scale=1">
7    <link href="https://fonts.googleapis.com/css?family=Open+Sans" rel="stylesheet">
8    <link href="{% static 'css/sb-admin-2.css' %}" rel="stylesheet">
9    <link href="{% static 'manager/css/structure.css' %}" rel="stylesheet" type="text/css">
10    <title>{% if request.path != '/' %}{% block title %}{% endblock %} | {% endif %}Blog App with Auth | Django2 Tutorial</title>
11</head>
12<body>
13<div class="container">
14    <header>
15        <nav>
16<ul>
17{% if user.is_authenticated %}
18<li><a href="{% url 'accounts:logged_out' %}" class="logged_out">Logout</a></li>
19{% else %}
20<li><a href="{% url 'accounts:signup' %}" class="SignUpView">Sign up</a></li>
21<li><a href="{% url 'accounts:login' %}" class="login">Login</a></li>
22{% endif %}
23</ul>
24</nav>
25</header>
26<div class="content">
27{% block content %}{% endblock %}
28</div>
29</div>
30
31</html>