It is possible to lose your unspent Smoldering Ashes just by changing world tiers or exiting character select. Once lost, your unspent Smoldering Ashes will no longer show in the seasonal tab and you will not be able to allocate them to any other character.
How to Fix Lost Smoldering Ashes
Leaving the game and then returning to the Character Select screen – This bug is resolved by exiting the game, re-entering the game, and exiting the Character Select screen again. We have confirmed this fix still works with Patch 1.1.1 after multiple tests have been conducted.
The other method that can be used to fix the bug is to exit the game completely and restart it from the beginning, which works similarly to exiting the character selection screen and then restarting the game.