Hi Oleh,
We have prepared a sample based on your requirement, but we were unable to reproduce the issue in the latest version(21.2.10). In order to better understand the issue you're facing, could you please modify the shared sample according to your scenario and provide us with the steps to replicate the issue, along with a video illustration sample if possible.
Regards,
Priyanka K
Attachment: Splitter_Blazor_1dd4535b.zip