Hazards

Weather
Without question the major hazard on this trek is the weather.
You need to be prepared (both in clothing, shelter and food) for cold, wet and potentially windy conditions. And that's in summer. On the other hand it can also be mild and sunny. Sometimes these follow one another within minutes. Changeable is the word. As there is no phone signal you would be well advised to get a good weather forecast before starting, and if you have concerns check with Hut Wardens who may have had a radio forecast.

On Kebnekaise itself the wind and cold combination can be severe, and you will need to dress accordingly.

Kebnekaise summit

Almost all the trail up Kebnekaise is very straightforward (at least under the conditions we experienced) BUT the summit itself (the last 25m or so) was a bit sketchy. It really merited crampons and an ice ax. Indeed we saw someone putting on crampons as soon the snow started. There was a high wind with very low visibility, and a slope on either side that disappeared into nothing. It required a deal of care in normal hiking shoes. On the other hand this was barely 300m of walking in 160km, and probably on a fine day would be pretty straighforward.

River crossings
We did not encounter any difficult river crossings, though as always these need to be executed carefully. On day 9 there was the option to take a bridge but most people we saw went straight and walked through the river.

Mosquitoes
These can be a major annoyance in particular seasons. However there is some relief. They don't much like cold and wind. They were not present higher up. They are very slow. The bite doesn't seem to itch much. That may be purely personal, but certainly they seemed less annoying than either midgies in Scotland or sandflies in NZ. I used a head net a few times and was very glad of it; also a strong DEET repellent when necessary. This wasn't as bad as I feared, but it can make cooking outside the tent a bit testing if it is warm.

Getting help
We had no phone signal for the entire trip, but then we didn't try on any summits. The Mountain Huts are the obvious contact point in the event of an emergency. Some (all?) of these have radios. There are no access points other than Nikkaluokta between the start and finish. However this northern section is well frequented in season. Further south that may be a different story altogether.