Aborting download of URL using web_stream_open with HTTP/HTML

Hej,

I'm getting in contact with the streaming feature the first time and I tried to test 2 examples.

1) URL = https://www.w3schools.com/html/mov_bbb.mp4

2) URL = https://www.w3schools.com/html/movie.mp4

The seconds one is working just fine. The first one keeps producing following error:

    Action.c(3): Aborting download of URL "https://www.w3schools.com/html/mov_bbb.mp4" (RelFrameId=1, Internal ID=1) (e.g., due to the target document or object being deleted) [MsgId: MMSG-26507]

and

Action.c(3): Notify: Transaction "1:BUFFERING" will be skipped - could not calculate the transaction time (duration=1.0532, think_time=0.0000, wasted_time=1.1124).

What is this output about? I get "web_stream_open was successful" but I'm not sure if it is really streaming ...
Help and hints appretiated :)

Greetings from Germany!