Not sure if you’d consider this a bug or expected behaviour, but…
When you cast let’s say 3 sigils of hope, they last for 15 seconds without buffs. If you refresh one after 10 seconds than the other 2 will still expire 5 seconds later, rather than refreshing the stack.
I don’t know if this is intended, but I’d suggest changing it so the entire stack gets refreshed. That will allow for smoother gameplay and allows you to keep going rather than so frequently having to stop to refresh your stacks.