Thank you for using Syncfusion products.
We have analyzed the issue and are unable to reproduce the issue according to the image one shared by you . So We have provided a sample for inserting a watermark using XlsIO. We also provided the KB link for further reference. Kindly refer the following link and get back to us if the issue is reproducing. If not, please modify the sample to reproduce the issue and get back to us. This will help us to investigate further and provide you a prompt solution.
We would request you to use our Direct-Trac Support system for further follow up.Kindly use the below link to login on Direct trac.
We were able to reproduce the problem and have logged defect report regarding this. A support incident to track the status of this defect has been created under your account. Please log on to our support website to check for further updates
Please let me know if you have any questions.