We updated Go (or more accurate: The Go template package) which fixed a bug which now correctly marks this as a logical error:
{{ if ( $.Page.IsMenuCurrent "main" .) ( $.Page.HasMenuCurrent "main" .) }}
In short: The result of what’s inside parens can never be a function and should never have arguments.
I assume the above should be:
{{ if (or ( $.Page.IsMenuCurrent "main" .) ( $.Page.HasMenuCurrent "main" .)) }}