From your article:
In summary, the data that I received from TTN seems a bit odd to me. Of course I could imagine explanations for all the odd cases I encountered but to my eye the data just does not look 100% right. This might be due to a bug hidden in my code or TTN or (and more likely) due to my lack of experience with Lora signal propagation in urban environments.
For what I understand, the latter is key; you’re (at least) running into reflection/multipath problems?
Aside: there’s a lengthy discussion in Location by triangulation.