Hi Constantine,
Greetings from Syncfusion.
We have validated your query and we can able to reproduce the reported problem at our end. We have confirmed it as a bug and logged the defect report for the same “Incorrect checkbox list shown in Excel/Checkbox filter dialog when filtering more the one column” . Thank you for taking the time to report this issue and helping us improve our product .Fix for the issue will be included in our weekly patch release which is expected to be rolled on or before end of November, 2020.
You can now track the current status of your request, review the proposed resolution timeline, and contact us for any further inquiries through this link.
Until then we appreciate your patience.
Regards,
Rahul
