Hi,
In Concrete5 version 5.7+ there is this newly added option at block editing ui:
"Design & Custom Template: Block Container Class" which Enable/Disable Grid Container.
The problem is "Migration Tool" package (https://github.com/concrete5/addon_migration_tool) does not respect the value of this select box. When i check the exported xml, there is no node for this value. I reported it at issue section of this package github (https://github.com/concrete5/addon_migration_tool/issues/29), but it seems it wasn't fixed on new versions.
I just want to report it here too, so maybe someone from core team take a look at it.