You're calling the field cellclasses, which is a sub-field of a group style. So the function rwmb_meta returns nothing, thus the next foreach loop doesn't work.
You should get the value of the group style first, then get the value of sub-field. Like this:
Thanks so much Anh, I didn't know that groups will affect how to display fields on the website.
Now works very well.
One more thing is that when adding multiple keys/values to select advanced the Metabox Builder does not create an array but a unique value, if I input the following on the options field:
Red: red
Yellow: yellow
Blue: blue
The Buuilder creates this and not an array:
'options' => 'Red: red
Yellow: yellow
Blue: blue',
Anh - note that it's not just select_advanced that is buggy when added to a group. It's also the regular select field that shows the same behavior when placed into a group using Builder. Perhaps fixing one will fix the other. Just wanted to make sure you knew it was both field types that did this.
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