The button mechanism wears out over time.
Has more difficulty in the cold.
You can buy a new switch and have it installed ... or make do with the FCD button as a trip meter.
The trip and km/mi buttons on the right are both part of the same part ... this is the same part in the dash as the opposite left side two buttons for dash.
And I once took mine from the left side to replace the trip meter one on the right side ... eventually it too wore out and now I just use the FCD.
Most of the replacement is the labor involved in access to it.
In the combination meter section ... the right and left side buttons are #10 and #11 .. 78147-S3Y-003 ... and 78148-S3Y-A01 ... although they are interchangeable with each other ... The part itself is ~$30 ... but labor to get to it is a pain in the ass.
If it is not the Switch chip itself ... the other remaining option is that there is a issue of some kind in the main display panel ... which is much more expensive.
But my bet is on a bad switch ... especially if after all these years you haven't changed yours yet.