HTTP response from upstream proxy (Cntlm) only correct if Burp Proxy used as intermediary proxy?

HTTP response from upstream proxy (Cntlm) only correct if Burp Proxy used as intermediary proxy?

I'm using a browser setup as follows:

Browser -> Burp -> Cntlm

For some reason, if I remove Burp from the equation and use Cntlm directly, then some webpages won't get displayed correctly, as can be seen below.

Anyone that has experienced something similar?

Browser -> Burp -> Cntlm

HTTP/1.1 200 OK
Cache-Control: no-cache
Pragma: no-cache
Content-Type: text/html;charset=utf-8
Vary: Accept-Encoding
Server: Microsoft-IIS/8.5
X-UA-Compatible: IE=EmulateIE9
X-UA-Compatible: IE=EmulateIE9
Date: Mon, 29 Jul 2019 14:33:41 GMT
Content-Length: 210
Proxy-Connection: keep-alive
Connection: keep-alive

{success:false,status:'5',userId:'0',isPartitionUser:false,loginMessage:'',message:'',reason:'',isICMUser:'0',isIntegrationEnabled:'false',time_frame_pref:'null',isSSOEnabledForUser:'true',isSSOLogin:'false'}

Browser-> Cntlm

HTTP/1.1 200 OK
Cache-Control: no-cache
Pragma: no-cache
Content-Type: text/html;charset=utf-8
Content-Encoding: gzip
Vary: Accept-Encoding
Server: Microsoft-IIS/8.5
X-UA-Compatible: IE=EmulateIE9
X-UA-Compatible: IE=EmulateIE9
Date: Mon, 29 Jul 2019 14:22:24 GMT
Content-Length: 259
Proxy-Connection: keep-alive
Connection: keep-alive

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