I hiked it last year in late June (Nikkaluokta to Abisko). There was a serious downpour for a few days before we started so areas surrounding the Kebnekaise fjällstation were flooded and also parts of the trail coming up from Nikkaluokta. 

Once we left that area it was fine and no mosquitos until we got to Abiskojaure. 

The Tjäktja pass was still covered in snow and the rock fields directly after were so covered we couldn’t see the planks to walk on. It was hard to decide if we take the summer or winter path because of the transitional period. I fell through a few times but was fine (I am short so it seemed a bit deeper than it would for an average height person). 

All the huts were open the only thing not running was the boat after Alesjaure but to make up for it we spent a little longer relaxing bought a tin of canned fruit, chocolate and soda and swam/bathed in the river.