This is a regression of MDL-61960, that was integrated only for 3.6. Carrying information from there:

Note that a regression with this patch has been detected. To reproduce:

• Have a non-working rss feed in your site (you can edit one of the current ones to make it fail).
• Run:

  php admin/tool/task/cli/schedule_task.php --execute=\\block_rss_client\\task\\refreshfeeds

• You get:

  http://xxx.xxx.xxx.xxx/rss.xml PHP Notice: A feed could not be found at `http://xxx.xxx.xxx.xxx/rss.xml`; the status code is `503` and content-type is `text/html; charset=utf-8` in /lib/simplepie/library/SimplePie.php on line 1702

  Default exception handler: Exception - Class 'block_rss_client' not found Debug:

  Error code: generalexceptionmessage

  * line 101 of /blocks/rss_client/classes/task/refreshfeeds.php: Error thrown

  * line 156 of /admin/tool/task/cli/schedule_task.php: call to block_rss_client\task\refreshfeeds->execute()

  !!! Exception - Class 'block_rss_client' not found !!!

• Proposed solution 1, tested locally, just add the missing classes needed when a rss fails:

  diff --git a/blocks/rss_client/classes/task/refreshfeeds.php b/blocks/rss_client/classes/task/refreshfeeds.php

  index 3e34e1b183..0feb681bd3 100644

  --- a/blocks/rss_client/classes/task/refreshfeeds.php

  +++ b/blocks/rss_client/classes/task/refreshfeeds.php

  @@ -66,6 +66,8 @@ class refreshfeeds extends \core\task\scheduled_task {

  public function execute() {

  global $CFG, $DB;

  require_once($CFG->libdir.'/simplepie/moodle_simplepie.php');

  + require_once($CFG->dirroot . '/blocks/moodleblock.class.php');

  + require_once($CFG->dirroot . '/blocks/rss_client/block_rss_client.php');

  // We are going to measure execution times.

  $starttime = microtime();

• Proposed solution 2, move the calculate_skiptime() method to the task, so no instantiation of the block is needed. It seems it's not used elsewhere.

Ciao