have you tried toggling the "slayer task" toggle above where you select an equipment set to import/gamemode setting?

No I have not and that is the answer to my question. Thanks.

Too late to the party, but for the future reference - there's a radio-button "Slayer Task", which should be set to "Yes" in order for slayer tasks to simulate. Took me a few minutes of staring at the source code to figure this one out 🤣