OK, you are on the 18.06-branch and not on the latest snapshot ... few days ago, there was a treewide change to convert HTML tables to div based markups (together with additional styling changes) in LuCI, see here. These changes are not in 18.06 tree - @jow any plans to backport this to 18.06?
Options for you:
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Stay with the 3.5.2 frontend (preferred option from my point of view). You can use this together with 3.5.3 backend without any problems. For a download look here: https://downloads.openwrt.org/releases/packages-18.06/x86_64/luci/
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Switch to latest snapshot builds