Thanks. Issue due to all website reorganization. Fixed.
I am also seeing this error. Just checked after noted fixed.
# Internal server error
url `'https://eu.swi-prolog.org/pack/query'' does not exist (status(500,Internal Server Error))
In:
[20] throw(error(existence_error(url,'https://eu.swi-prolog.org/pack/query'),context(_774,...)))
[18] http_open:try_http_proxy(direct,[uri('https://eu.swi-prolog.org/pack/query'),...|...],_810,[method(get),...|...]) at /usr/lib/swipl/library/ext/http/http/http_open.pl:505
[16] plweb_proxy:proxy(get,"https://eu.swi-prolog.org",[protocol(http),...|...],[request_headers(...)]) at /srv/plweb/proxy.pl:80
[13] pack:pack_query([protocol(http),...|...]) at /srv/plweb/pack.pl:82
[12] http_dispatch:call_action(pack:pack_query,[protocol(http),...|...]) at /usr/lib/swipl/library/ext/http/http/http_dispatch.pl:1043
[10] time:run_alarm_goal('$alarm'(94353470318704),http_dispatch:call_action(...,...,...)) at /usr/lib/swipl/library/ext/clib/time.pl:163
[9] setup_call_cleanup(time:alarm(300,...,...,...),time:run_alarm_goal(...,...),time:remove_alarm_notrace(...)) at /usr/lib/swipl/boot/init.pl:682
[5] httpd_wrapper:call_handler(http_dispatch:time_limit_action(...,...,...),160860,-) at /usr/lib/swipl/library/ext/http/http/http_wrapper.pl:323
[4] catch(httpd_wrapper:call_handler(...,160860,-),error(existence_error(url,'https://eu.swi-prolog.org/pack/query'),context(_1228,...)),httpd_wrapper:true) at /usr/lib/swipl/boot/init.pl:565
[3] httpd_wrapper:handler_with_output_to(http_dispatch:time_limit_action(...,...,...),160860,-,current_output,error(existence_error(url,'https://eu.swi-prolog.org/pack/query'),context(_1304,...))) at /usr/lib/swipl/library/ext/http/http/http_wrapper.pl:308
Note: some frames are missing due to last-call optimization.
Re-run your program in debug mode (:- debug.) to get more detail.
[SWI-Prolog](http://www.swi-prolog.org/) httpd at 2cf4018713c9
Everything is fine now (as far as I can tell). You still get this. /pack/query uses Content-type: x-prolog and is used by pack_install/2, etc. The only problem is that it should reply with a bad request status if you try to query it from a browser.
Where were still some pending errors from the CDN cache. These should disappear completely in the next hour. Using the current git version you can do
swipl pack find --server=eu.swi-prolog.org <string-to-find>
Or us.swi-prolog.org, which proxies back to eu.swi-prolog.org or www.swi-prolog.org, which causes the CDN to query one of the two backends.
That works as expected.
C:\Users\Groot>swipl pack find --server=eu.swi-prolog.org matrix
% Contacting server at https://www.swi-prolog.org/pack/query ... ok
p ffimatrix@0.1.0 - Operations with matrices using Prolog and C
U matrix@1.0(2.0) - Operations with matrices
p matrix_utls@1.1 - Matrix utilities: Kronecker (Tensor), Hadamard, and matrices creation/multiplications
C:\Users\Groot>
However the other two currently return error. I’ll try again after an hour. 
C:\Users\Groot>swipl pack find --server=us.swi-prolog.org matrix
% Contacting server at https://www.swi-prolog.org/pack/query ...
ERROR: c:/program files/swipl/app/pack.pl:39: user:main url `'https://www.swi-prolog.org/pack/query'' does not exist (status(500,Internal Server Error))
C:\Users\Groot>swipl pack find --server=www.swi-prolog.org matrix
% Contacting server at https://www.swi-prolog.org/pack/query ...
ERROR: c:/program files/swipl/app/pack.pl:39: user:main url `'https://www.swi-prolog.org/pack/query'' does not exist (status(500,Internal Server Error))
Works for me. Note that in your examples they all address www.swi-prolog.org as the release still ignores this option. You need to build from the current git source.
And impossible to load the real and b_real packs.
How can I manage SSL erro : certificate verify failed ?
I am running on Windows11 with the latest Swipl 9.3 64bts
Thank you in advance
JAcques
Yes. Experienced the same installing some packs on one of the new servers 
Looks like some sort of issue talking to nginx HTTPS servers without connection('Keep-alive').
Use pack_install/2 with the insecure(true) option. This is a problem with the upstream HTTPS server. Older versions did not check the certificate. I think we should check certificates these days.
Thank you Jan,
I will check pack_install/2 as soon the server is stable.
Best regards, all the best and ‘Bravo’ for your work on Swipl
Jacques
After some 4-5 attempts it worked.
Thank you.
Remains now the connection between ‘real’ and ‘R’ which was allways complicated on windows…
Thanks
Better than never … Pushed some updates that might resolve this. At least, in a first sequence of trials all worked fine. The core fixes are in the HTTP client library. One is related to the possibility to generate an exception on Keep-alive connections and the other is to avoid TLS handshake issues by reading Content-length bytes and then simply close, ignoring any error. It seems some servers do the same, so hoping on a clean TLS EOF handshake is not a good idea.
Nginx still has an open source version that is in most Linux distros. For a comparison, see e.g. Compare NGINX Open Source OS vs Plus - Free vs Paid - WorldTech IT The SWI-Prolog web services are partly based on virtual hosts and nginx is an excellent proxy server. All we need is a proxy server that scales well, can do load balancing (for next SWISH deployment), can do websockets and can handle Letsenscript! certbot. The standard Linux version of nginx does all that. If something goes wrong, there are probably alternatives.