I have the Helix Ultimate with J5.3 and the latest build of SPPB. Now to be clear everythign worked perfectly. I added a button group. I formatted a single button the way I wanted to have it appear, saving and previewing each time. Once happy I duplicated this button 2 further times, so I have 3 buttons all identical. Changed the button text etc, leaving the links out as I had not yet created the links, save and preview all looking perfect

I then put in some text to the link, I know it wont work as the page does not exist yet, and save, and as soon as I preview it I get the below errors.

Object of class stdClass could not be converted to string /sppagebuilder/addons/button_group/site.php:32

The line in question is this

32 $attribs .= (isset($value->url) && $value->url) ? ' href="' . $value->url . '"': '';

I would have expected the link to not work but I did not expect it to error. the most annoying part is that even if I delete the link information it will no longer work without error, the only way to fix it is to delete the entire button group and start over