Short helps, but 17 dB is not „short trace“ territory, that’s a broken RF path. Did this on a sensor board for a cleanroom monitor and lost about the same.
Questions to check: is there solid ground under the trace on the other layer? Is the trace 50 ohm? On 1.6 mm FR4 a 50 ohm microstrip is around 3 mm wide, so a 0.25 mm signal trace is closer to 120 ohm. Over 6 mm that alone isn’t the whole 17 dB, but add no ground plane under it and the trace is half an antenna radiating into your own board.
What I’d do on the next revision: coplanar waveguide with ground on both sides and a row of vias, width from a calculator for your stackup, a pi network footprint between module and connector (0 ohm in series, others not fitted until you can measure), and the U.FL ground pads stitched straight to the plane. Keep the switching regulator away from that corner.
Then compare again in the frames log, it shows the best RSSI and SNR per uplink so you can check both boards on the same gateway without extra tools. See The frames log.