Google Docs is a rich text editor which means they’re pasting in a whole bunch of invisible formatting that usually doesn’t play well with non rich-text destinations (from my experience).
I paste from GDocs all the time. It’s part of my publishing workflow.
Keep your source simple; paragraphs, blockquotes, headings, bold, italics, lists.
Webflow had an issue at one point after adding the Markdown support, where on paste it would mis-identify some pasted content as Markdown and you’d see a dramatically different result. I think that’s been disabled as a clipboard-paste feature, but if they’ve re-enabled it, it’s possible you’re content could be tripping it up somehow.
If you use Windows, try CTRL+SHIFT+V, typically it will paste the plaintext only version from the clipboard. I think that’s an app-level feature rather than a Windows-level feature, but Chrome ( at least ) seems to support this.