We started getting a preg_match Visual Composer PHP error that was: Warning: preg_match() expects parameter 2 to be string, array given in /wp-content/themes/bridge/vc_templates/vc_empty_space.php on line 12.
I was able to determine that when using the empty space feature for managing site contents in the design, if you saved “px” in the pixel value for the size of the empty space, WordPress results would throw this error. For example, if I saved 16px for the size, we would get this error message. However, if I went back in and just saved the value as 16 the system would work as expected.
This is only a slight fix, I have discovered that in a recent update to Visual Composer, the issue was resolved. So be sure you have updated to (at this time) v4.8
Here is a quick link to the Visual Composer plugin.