Dear Sir,
As per L86 hardware design, its static horizontal positioning accuracy is 2.5m@CEP50. No extra configuration to reach best performance.
Generally, drift on performance is about 10-200 meters. 1 km error might be caused wrong calculation of lat/long, offset in some maps or different coordinate system.
Could you provide true value point and your test log? I can help check.
BTW, you could use QGNSS to check.
Regards