Hi Ravimama,
Base on my understanding, when you open the form in VS designer, a user control hosted in TabControl cannot shown correctly, but it does shown correctly in run time. Am I right?
It seems the user control in another assembly cannot be loaded correctly in design time and cause the problem. Please try to keep that user control opened in the designer when you open the form. This can ensure the VS designer load the user control from the assembly correctly.
Please tell me if it helps.
Sincerely,
Kira Qian
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