This could be a particular GPS bug1 - I can't find any reference right now but I have come across one of these before (years ago, when Foursquare first came out) that always affected one particular position (Melbourne Central Station in Melbourne, Australia), and which reported it - for everyone - at Glen Waverley, a suburb about 30 kilometres away.
You could be seeing something similar to this. If you can't avoid it, I would first:
- try to work out whether it is happening to anyone else
- gather some data about when and where it has happened to you (include times, map screenshots, etc.)
- report to Niantic that you're getting a soft ban when you don't believe you should
If it is a GPS bug1, Niantic aren't going to be able to fix it, but perhaps they can lift your soft bans. If you can prove that this is happening to others as well, then this may assist you further - particularly if others are getting soft bans as well.
1 Not technically a GPS bug, but rather a problem with using WiFi routers to augment GPS (hat tip to Loren Pechtel)