saguaros
Here is what I remember. More or less both times times it happened.
Downloaded Build.r 1.3.9 and installed perhaps 3 weeks ago (early October 2018).
Experienced the problem once with Joomla 3.8.something and yesterday with J 3.9
Steps to cause the failure were relatively similar in both cases:
Loaded a template from the Load Saved Settings dropdown once OnePageTwo and once Backgrounder.
Modified various template settings for several hours, saving every few minutes.
On the Design tab I loaded the ABOVECONTENT module into abovecontent template slot.
Immediatly got the warning: Warning: Invalid argument supplied for foreach() in /var/www/html/sunflowermesa.com/public_html/templates/buildr/zengrid/zen.php on line 1433
All slots and all modules in all slots in the template designer widget (blue top bar and template positions for modules) went utterly blank. Website front end completly stopped functioning - showing that same warning.
Nothing I did after that restored the template. My only option was to LOAD SAVED SETTINGS and start over from scratch. All my changes were lost.
The experience with OnePageTwo was similar, i.e. attempted to load a module into a slot and bam, lost all setting which are stored, I presume, in a JSON file, which was probably corrupted at that point somehow.