LoRa should easily manage 250m baseline IF nothing blocks the signal like obstacles or noise.
The first thing I would do is a range test in an open area where the base is rised, like on top of a building or hill, providing line of site to the rover.
You should range at least 1000m with no issues.
Also, Fresnel zone is real and greatly impact the range of your signals, Fresnel zone - Wikipedia
Even though you made it work before in the same area, the situation might be difference now, more dense vegetation, higher vegetation, new introduced RF noise, different or changed contruction near by etc. In my experience it takes very little to disrubt lora signals when you dont have line of sight to the base.
Way back we did a range test hitting over 50km baseline, for your refrence.