Here's something I've never seen discussed, but I,ve been kinda curious about.
- The content of the linked page on a GBP will affect majorly the ranking for the GBP, this is well established.
- Certain technical factors (e.g. multiple cross-domain redirects, 404 error, url frame cloaking) will cause Google to just up and remove the URL. (I have personally ran into all three cases.)
- It's also well established that any organic ranking of the page in general has no effect on GBP ranking.