Fix rare networking edge case that can cause scheduler thread to get into a bad state, fixes #2866

lib/sidekiq/scheduled.rb

@@ -86,6 +86,13 @@ module Sidekiq
       def wait
         @sleeper.pop(random_poll_interval)
       rescue Timeout::Error
+        # expected
+      rescue => ex
+        # if poll_interval_average hasn't been calculated yet, we can
+        # raise an error trying to reach Redis.
+        logger.error ex.message
+        logger.error ex.backtrace.first
+        sleep 5
       end
 
       # Calculates a random interval that is ±50% the desired average.