Accessing URL from travis windows/linux yields 403 permission denied

I started to move my windows builds from Appveyor to travis and I can’t get the unit tests I run to work. At the same time I started to build my project also for linux with the same issue that loading a resource from a specific URL always yields a 403 permission denied.
I run these tests for month on travis osx machines and Appveyor.

An example URL is:
https://download.unity3d.com/download_unity/6d84dfc57ccf/unity-2017.4.9f1-win.ini

If I curl the file in the build script it works most of the times. But not when I call it from my project.
I have no issues to execute these tests or the tool in question from any other machine I can test with.

the pull request to add windows support

the pull request to start building on linux

here a failing curl output:

% Total    % Received % Xferd  Average Speed   Time    Time     Time  Current
                                 Dload  Upload   Total   Spent    Left  Speed
  0     0    0     0    0     0      0      0 --:--:-- --:--:-- --:--:--     0*   Trying 23.66.96.60...
* TCP_NODELAY set
  0     0    0     0    0     0      0      0 --:--:-- --:--:-- --:--:--     0* Connected to download.unity3d.com (23.66.96.60) port 443 (#0)
* schannel: SSL/TLS connection with download.unity3d.com port 443 (step 1/3)
* schannel: checking server certificate revocation
* schannel: sending initial handshake data: sending 185 bytes...
* schannel: sent initial handshake data: sent 185 bytes
* schannel: SSL/TLS connection with download.unity3d.com port 443 (step 2/3)
* schannel: failed to receive handshake, need more data
* schannel: SSL/TLS connection with download.unity3d.com port 443 (step 2/3)
* schannel: encrypted data got 3679
* schannel: encrypted data buffer: offset 3679 length 4096
* schannel: sending next handshake data: sending 126 bytes...
* schannel: SSL/TLS connection with download.unity3d.com port 443 (step 2/3)
* schannel: encrypted data got 274
* schannel: encrypted data buffer: offset 274 length 4096
* schannel: SSL/TLS handshake complete
* schannel: SSL/TLS connection with download.unity3d.com port 443 (step 3/3)
* schannel: stored credential handle in session cache
> GET /download_unity/6d84dfc57ccf/unity-2017.4.9f1-win.ini HTTP/1.1
> Host: download.unity3d.com
> User-Agent: curl/7.55.1
> Accept: */*
> 
* schannel: client wants to read 102400 bytes
* schannel: encdata_buffer resized 103424
* schannel: encrypted data buffer: offset 0 length 103424
* schannel: encrypted data got 596
* schannel: encrypted data buffer: offset 596 length 103424
* schannel: decrypted data length: 567
* schannel: decrypted data added: 567
* schannel: decrypted data cached: offset 567 length 102400
* schannel: encrypted data buffer: offset 0 length 103424
* schannel: decrypted data buffer: offset 567 length 102400
* schannel: schannel_recv cleanup
* schannel: decrypted data returned 567
* schannel: decrypted data buffer: offset 0 length 102400
< HTTP/1.1 403 Forbidden
< Server: AkamaiGHost
< Mime-Version: 1.0
< Content-Type: text/html
< Content-Length: 354
< Expires: Mon, 24 Jun 2019 19:11:55 GMT
< Date: Mon, 24 Jun 2019 19:11:55 GMT
< Connection: keep-alive
< 
{ [354 bytes data]
100   354  100   354    0     0    354      0  0:00:01 --:--:--  0:00:01   754
* Connection #0 to host download.unity3d.com left intact
<HTML><HEAD>
<TITLE>Access Denied</TITLE>
</HEAD><BODY>
<H1>Access Denied</H1>
 
You don't have permission to access "http&#58;&#47;&#47;download&#46;unity3d&#46;com&#47;download&#95;unity&#47;6d84dfc57ccf&#47;unity&#45;2017&#46;4&#46;9f1&#45;win&#46;ini" on this server.<P>
Reference&#32;&#35;18&#46;ce3c4317&#46;1561403515&#46;1f096f73
</BODY>
</HTML>

Is it possible that they are blocking our IP addresses?

Sometimes some calls get through in the same test run. I am really lost.

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