This error is still occuring in February 2022 and has nothing to do with PHP settings, I think it has to do with nonc conflict with the plugin banner.  Click to close the banner permanently and this should be fixed. 

Yes turning off FastCGI does seem to help. Is FastCGI not better for speed etc. It's also the recommended default on Dreamhost.   updraftplus backup plugin seems to have no issues with this, I think because they break up the backup into separate zip files and thereby circumvent the limitations of most shared hosting/server environments.  Maybe something for site upkeep to consider as most people will not understand why their backups are failing on Dreamhost and will maybe ditch the plugin altogether. I almost did to replace it with  UpdraftPlus.  

Also,  what it does not explain is why on my shared starter hosting with Dreamhost I have no issues with site upkeep and am using FastCGI!  While on my unlimited shared environment I do have issues.  

UPDATE:  Set up a vanilla on-click install on Dreamhost same server, same settings using Boldgrid.  although the backups ran ok some of the time,  they still fail quite often. Mind you, this is unchanged vanilla install! 

UPDATE:   its actually failing with ZipArchive too.  so failing across the board.  

Figured this out,  reinstalled the site and all works fine now.  Might work too if you remove and reinstall the plugin...

OK, I figured this out.  You just need to get the premium key for your WordPress site and add it to your boldgrid central account.