Hello Robert,

Thank you for reporting this problem.

We identified this issue as being caused by the regression we introduced with the fix Excel-Like filtering of RadGrid throws an exception when the filter value starts with a question mark "?"

There is a fix available that will address both problems and is scheduled to be released for version R2 2022.

Until the fix is delivered, we can suggest downgrading the Telerik assemblies to a version prior to "R2 2021 SP1". 

Please accept our apology for any inconvenience this may have caused.

Regards,
Attila Antal
Progress Telerik