Hello,
We need to see your actions before you get that message. For example: you logged in to your account, went to shop, added product, visited any other page or what did you do before the error appears on your checkout page. How long does you serf through your site before you get this message? Could you, please, provide us with the video with this information? Not just the error. You can use Recordit tool to create and share the link to video.
Do you have the mentioned error when cache plugin is enabled or disabled?
Regards