In version 6.6.3 the queryfilter turned out like this:
it => (it.Header == null ? "" : it.Header).ToLower().Contains("filtervalue".ToLower())
The new version throws an error with a different filter that the internal parser does not handle.
It has something to do with the radzen parser. If I Explicitly use System.Linq.Dynamic.Core it works.
Like so: filteredData = DynamicQueryableExtensions.Where(filteredData, grid.Query.Filter);
Please use our demos to provide an example demonstrating your scenario and the problem you have with the filtering.