Task cancel by boundary timer event don't fire

I have process with multiple tasks. Each task has boundary timer and set cancel activity = true.
Some of tasks have assigned candidate group and some don’t in this manner:
First has, second hasn’t, third has, fourth has, fifth hasn’t, sixth hasn’t.
When I do nothing process goes this way: first to fourth task are canceled, fifth task is not canceled and it is stucked.
There is nothing in catalina.log. What is wrong? Can I see somewhere what is happend.

Can you share your process xml? The timer boundary should do the same for each user task, irregardless of its assignment state.

I cannot simulate this problem anymore.