The “Win __ Challenge Battles” task pops up several times. You have to beat “Win 1-4” once each but “Win 5” appears 5 times. If you havnt completed at least 35 challenges you may not have completed enough.
You can find a full list there and perhaps see exactly where you are on the list.
If I recall correctly on my alt account, the last task before the ‘Kill 100 Troops’ was to collect a Broken Spire Legendary troop. I had completed all the basic tasks and had to wait until Broken Spire week and used all my event keys (100ish or so). It was a loooong wait. More power to the actual newbies for sticking with the game.
I always recommend to any of my guild members above 150 to skip adventure path tasks that take more than a day to complete, such as getting broken spire to 5 stars, which depends on luck with a legendary troop, or leveling a pet to 10. Any gems you spend to skip will quickly be refunded when you complete the path and get the repeating daily task that rewards 20 gems, or 100 on a lucky day.