In this case, the cause of the issue most probably is somewhere else. I tried to reproduce this issue in our live demo
but the DropDown of the ComboBox did not move with the page when scrolled even when CloseDropDownOnBlur
I will need to first investigate your page. Could you paste here the code of the ComboBox and any custom CSS that is used by it? If the page is more complex, please consider opening a support ticket and sending us the files there.
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