I have also confirmed this. Bee Tycoon Island Code: 3597-8094-4458.
The “Secondary Ability + ADS” mobile button does not show when holding the remote item. This buttons needs to show.
Also it would be nice if there was a secondary ability button that was not combined with the ADS button for people that do not want a combined button. The ADS & Throw Consumable buttons are still available even though you could just use the combined button.
You should not be missing any information on how to reproduce this.
Start Fortnite Mobile.
Play Bee Tycoon Island Code: 3597-8094-4458
Once the game has started switch to the signal remote item.
While holding the item look for the “Secondary Ability + ADS” button on the screen. (The button name is from the HUD Layout Tool).
You will notice the button does not show on the screen for mobile. This button is needed for the secondary ability of the signal remote item. The fire button is used for the first ability and the “Secondary Ability + ADS” button is used for the secondary ability.