I was using Heroku PGbackups add-on for backup copying of DB from one Heroku app into another Heroku app. But after PGbackups migration and removal of their add-on, I moved these commands to using new commands according to instructions. But I am now encountering an issue with this process: sometimes pg:backups restore gets into pending status. The DB is cleared but the backup doesn't copy/restore and just stucks with 'pending'.
Here is what I got when checking the status of pg:backups 
At this time the Db was not overloaded with connections:
Then I used pg:wait command and previous requests failed and the new ones worked fine and did not get into pending 
But I am not sure if this will happen again.
I would be very grateful if you explain me what the reason might be and how to fix the issue. Thanks in advance for your time and help.