Same issue is being observed alarm app not working properly not sure is it related to clear all apps issue I spoke to Nokia support and followed their procedure still same issue of alarm after 24 he cycle not working but within 24 he cycle it works if some one has a fix do share
Solution for this issue is that, you have to add the app to battery optimization as "Not to Optimise". And Soft reset your phone.
Even Alarm app issue can do the same.
I had same issue, I tried this on my Nokia 6, now it works fine for me.