@Leon
I've just checked the http-header and found 2 404 errors - one of it could explain the empty page (the first 404 below). Do you understanding why your HTML was sending a request onto atarget which is not existing? Did you've changed anything?
That's what I did
Sent a http-request to the URL http://htmlpreview.github.io/?https://github.com/leonjessen/CPHRANNworkshop/blob/master/lectures/session_1_introduction_to_workshop.html and measure what happens from sending the request until receiving the result.
That's what I've found
https://cors.io/?https://raw.githubusercontent.com/leonjessen/CPHRANNworkshop/master/lectures/session_1_introduction_to_workshop.html
Host: cors.io
User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:68.0) Gecko/20100101 Firefox/68.0
Accept: */*
Accept-Language: de,en-US;q=0.7,en;q=0.3
Accept-Encoding: gzip, deflate, br
Referer: http://htmlpreview.github.io/?https://github.com/leonjessen/CPHRANNworkshop/blob/master/lectures/session_1_introduction_to_workshop.html
Origin: http://htmlpreview.github.io
Connection: keep-alive
GET: HTTP/2.0 404 Not Found
date: Mon, 26 Aug 2019 16:40:54 GMT
content-type: text/html; charset=utf-8
set-cookie: __cfduid=d19f370fe7519b1a498c156c32b5fc6b31566837654; expires=Tue, 25-Aug-20 16:40:54 GMT; path=/; domain=.cors.io; HttpOnly; Secure
cache-control: no-cache, no-store
expect-ct: max-age=604800, report-uri="https://report-uri.cloudflare.com/cdn-cgi/beacon/expect-ct"
server: cloudflare
cf-ray: 50c7400bfe00d6e9-FRA
content-encoding: br
X-Firefox-Spdy: h2
---------------------
http://htmlpreview.github.io/favicon.ico
Host: htmlpreview.github.io
User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:68.0) Gecko/20100101 Firefox/68.0
Accept: image/webp,*/*
Accept-Language: de,en-US;q=0.7,en;q=0.3
Accept-Encoding: gzip, deflate
Connection: keep-alive
GET: HTTP/1.1 404 Not Found
Server: GitHub.com
Content-Type: text/html; charset=utf-8
ETag: W/"5c1d106f-247b"
Access-Control-Allow-Origin: *
Content-Security-Policy: default-src 'none'; style-src 'unsafe-inline'; img-src data:; connect-src 'self'
Content-Encoding: gzip
X-Proxy-Cache: MISS
X-GitHub-Request-Id: 1AC2:62C2:7A058A:A906E1:5D64018F
Content-Length: 5232
Accept-Ranges: bytes
Date: Mon, 26 Aug 2019 16:40:54 GMT
Via: 1.1 varnish
Age: 2567
Connection: keep-alive
X-Served-By: cache-hhn4073-HHN
X-Cache: HIT
X-Cache-Hits: 1
X-Timer: S1566837654.294923,VS0,VE0
Vary: Accept-Encoding
X-Fastly-Request-ID: 2c0042552a9e66ba8cb42d55711045d285f90626