Take my apologies for the delay in answering.
We checked your site and see that your child theme includes a lot of custom code, custom styles and libraries. Once we enable parent theme we don’t see any blinking. It appears only when your custom theme is enabled. You can enable the parent theme and check by yourself. So, probably the additional customization you made causes the issue but we are not developers who made that customization. So, ask the developer who made that customization to check the additional libraries and custom styles that he used (turn them off and check which one causes the issue).
One standard license is valid only for 1 project. Running multiple projects on a single license is a copyright violation.