It does repeat if I hit sync again. Running with debug flags, I don’t see any output to the console, but the log.txt contains the following as the most recent event:

2019-02-28 20:06:06: "Sync: finished: Synchronisation finished [1551413165013]"
2019-02-28 20:06:06: "Reducer action", "SYNC_REPORT_UPDATE"
2019-02-28 20:06:06: "Operations completed: "
2019-02-28 20:06:06: "createRemote: 1"
2019-02-28 20:06:07: "Total folders: 2"
2019-02-28 20:06:07: "Total notes: 783"
2019-02-28 20:06:07: "Total resources: 30"
2019-02-28 20:06:07: "There was some errors:"
2019-02-28 20:06:07: "SyntaxError: OneDriveApi::exec: Cannot parse JSON error: <!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<meta http-equiv="Content-Type" content="text/html; charset=iso-8859-1"/>
<title>404 - File or directory not found.</title>
<style type="text/css">
<!--
body{margin:0;font-size:.7em;font-family:Verdana, Arial, Helvetica, sans-serif;background:#EEEEEE;}
fieldset{padding:0 15px 10px 15px;} 
h1{font-size:2.4em;margin:0;color:#FFF;}
h2{font-size:1.7em;margin:0;color:#CC0000;} 
h3{font-size:1.2em;margin:10px 0 0 0;color:#000000;} 
#header{width:96%;margin:0 0 0 0;padding:6px 2% 6px 2%;font-family:"trebuchet MS", Verdana, sans-serif;color:#FFF;
background-color:#555555;}
#content{margin:0 0 0 2%;position:relative;}
.content-container{background:#FFF;width:96%;margin-top:8px;padding:10px;position:relative;}
-->
</style>
</head>
<body>
<div id="header"><h1>Server Error</h1></div>
<div id="content">
 <div class="content-container"><fieldset>
  <h2>404 - File or directory not found.</h2>
  <h3>The resource you are looking for might have been removed, had its name changed, or is temporarily unavailable.</h3>
 </fieldset></div>
</div>
</body>
</html>
 Unexpected token < in JSON at position 0
SyntaxError: OneDriveApi::exec: Cannot parse JSON error: <!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<meta http-equiv="Content-Type" content="text/html; charset=iso-8859-1"/>
<title>404 - File or directory not found.</title>
<style type="text/css">
<!--
body{margin:0;font-size:.7em;font-family:Verdana, Arial, Helvetica, sans-serif;background:#EEEEEE;}
fieldset{padding:0 15px 10px 15px;} 
h1{font-size:2.4em;margin:0;color:#FFF;}
h2{font-size:1.7em;margin:0;color:#CC0000;} 
h3{font-size:1.2em;margin:10px 0 0 0;color:#000000;} 
#header{width:96%;margin:0 0 0 0;padding:6px 2% 6px 2%;font-family:"trebuchet MS", Verdana, sans-serif;color:#FFF;
background-color:#555555;}
#content{margin:0 0 0 2%;position:relative;}
.content-container{background:#FFF;width:96%;margin-top:8px;padding:10px;position:relative;}
-->
</style>
</head>
<body>
<div id="header"><h1>Server Error</h1></div>
<div id="content">
 <div class="content-container"><fieldset>
  <h2>404 - File or directory not found.</h2>
  <h3>The resource you are looking for might have been removed, had its name changed, or is temporarily unavailable.</h3>
 </fieldset></div>
</div>
</body>
</html>
 Unexpected token < in JSON at position 0
    at JSON.parse (<anonymous>)
    at OneDriveApi.exec (C:\Users\philm\AppData\Local\Programs\Joplin\resources\app.asar\lib\onedrive-api.js:188:27)
    at process._tickCallback (internal/process/next_tick.js:68:7)"
2019-02-28 20:06:07: "Reducer action", "SYNC_COMPLETED"
2019-02-28 20:06:07: "Setting up recurrent sync with interval 300"