Thanks for using Syncfusion Products.
We suggest you to use up/down arrow keys to change the values of the dropdown when you editing a cell. We have prepared a video demonstration for this and the same can be downloaded from the below link.
Please let us know if you need any further assistance.
Thanks for the update.
We are sorry for the inconvenience caused.
We are able to reproduce your issue in our end (pressing down/up arrow keys in dropdown then the values are changed but the selection moves to next/previous rows). We have prepared a video to demonstrate this and the same can be downloaded from the below link.
Could you please have a look at the above video and confirm whether you are facing the same in your end?
Please let us know if you have any concerns.
Alan Sangeeth S