Trouble saving settings via Mission Planner using MavLink

APM 2.6, FW 3.2.1, Mission Planner 1.3.31.

When connecting using Mavlink wireless I get all information, settings etc. But when changing settings, e.g. calibrating compass or changing Flight modes - when hitting the save-button I get an error-message saying “error saving parameter”, and the settings isn’t saved.

So, to solve this I’m just using the USB-cable, but I’d really like to be able to change settings using MavLink wireless-connection as it’s really hard to reach the USB-output.

Anyone having the solution or any tip?