If the igniition key unlocks on both the fuel cap and the seat lock without any problem, and the spare key also has difficulty in turning the ignition switch on, chances are that the key barrel is damaged or somehow restricted.
If you are under the group that have a multiple keys on your keyring, it is possible that the weight combined with vibration, etc, has slowly caused a wafer or more to deform.
One would automatically think it would be best to replace the ignition switch at this stage. In some countries, the ignition key contains a transponder, that is matched to the bike's ECU. Making this option expensive to replace.
A possible work around, is to remove the ignition switch barrel. Once the barrel is on your work-bench, you can see whether any of the wafers are standing proud, thus binding when the key is turned. If any wafers are deformed / not flush with the barrel, you can file a bit off the wafe with the key in the barrel or remove one wafer at a time for a closer inspection
A special note: each of these wafers are spring loaded, so take care as not to loose any of these small springs. Also there is often a spring loaded ball bearing in the electrical part of the switch that locates the switch positions.
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