Add core results in AJAX error

Issue #3143066 on drupal.org by amykhailova.

Go to the Add Core tab (drd/cores/add), add a site URL and press tab.
Open browser console you should see the AJAX error

"
An AJAX HTTP error occurred.
HTTP Result Code: 200
Debugging information follows.
Path: /drd/cores/add?ajax_form=1
StatusText: parsererror
ResponseText: * Found bundle for host example.com: 0x2cc2390
* Re-using existing connection! (#0) with host example.com
* Connected to example.com (104.26.3.239) port 443 (#0)
> POST /drd-agent-crypt HTTP/1.1
Content-Length: 0
User-Agent: Drupal/8.8.6 (+https://www.drupal.org/) GuzzleHttp/6.3.3 curl/7.40.0 PHP/7.3.15
Host:  example.com
X-Drd-Version: 1.7.0
POST /drd-agent-crypt HTTP/1.1
Content-Length: 0
User-Agent: Drupal/8.8.6 (+https://www.drupal.org/) GuzzleHttp/6.3.3 curl/7.40.0 PHP/7.3.15
Host:  example.com
X-Drd-Version: 1.7.0
< HTTP/1.1 200 OK
< Date: Tue, 26 May 2020 20:27:06 GMT
< Content-Type: text/plain; charset=utf-8
< Transfer-Encoding: chunked
< Connection: keep-alive
< Set-Cookie: __cfduid=db741a92d4d6d011a524e3a8fcaea5f521590524826; expires=Thu, 25-Jun-20 20:27:06 GMT; path=/; domain= example.com; HttpOnly; SameSite=Lax; Secure
< Cache-Control: must-revalidate, no-cache, private
< Content-Language: en
< Expires: Sun, 19 Nov 1978 05:00:00 GMT
< X-Content-Type-Options: nosniff
< X-Drd-Agent: 1.7.0
< X-Frame-Options: SAMEORIGIN
< X-Generator: Drupal 8 (https://www.drupal.org)
< X-Pantheon-Styx-Hostname: styx-fe3-b-c8f8fbbbb-jp5mj
< X-Styx-Req-Id: 4439a68c-9f8f-11ea-bd03-f2cc0323dd98
< X-Ua-Compatible: IE=edge
< X-Served-By: cache-mdw17347-MDW, cache-yyz4545-YYZ
< X-Cache: MISS, MISS
< X-Cache-Hits: 0, 0
< X-Timer: S1590524826.182749,VS0,VE71
< Vary: Accept-Encoding,
< Age: 0
< Via: 1.1 varnish
< CF-Cache-Status: DYNAMIC
< cf-request-id: 02f443ea440000caa0878f9200000001
< Expect-CT: max-age=604800, report-uri="https://report-uri.cloudflare.com/cdn-cgi/beacon/expect-ct"
< Server: cloudflare
< CF-RAY: 599a3c23a9d0caa0-YYZ
< 
* Connection #0 to host  example.com left intact
[{"command":"update_build_id","old":"form-rVqkZofXgMDY_McagziwJNjEYt4BcN-F0LOqf3ch7ro","new":"form-rR3OiKaUR1O-Vku4kV44xB05kKEvVIrUDpCAVXA2me0"},{"command":"invoke","selector":"#edit-drd-crypt-type option[value=\u0022OpenSSL\u0022]","method":"prop","args":["disabled",false]},{"command":"invoke","selector":"#edit-drd-crypt-type option[value=\u0022TLS\u0022]","method":"prop","args":["disabled",true]},{"command":"invoke","selector":"#edit-drd","method":"removeClass","args":["hidden"]},{"command":"invoke","selector":"#edit-actions","method":"removeClass","args":["hidden"]},{"command":"insert","method":"html","selector":"#edit-url-message","data":"","settings":null}]"

So essentially after that AJAX returns with error and callback isn't finished.