This is expected behaviour when using the tool and is the same with a mouse or when using a touchpad. I believe due to the sensitive input from a touchpad that Affinity is detecting a 'tap' on the canvas as a very small click and drag movement, which sets the tolerance to 1%.
Thanks for letting me know, we've seen that disabling Windows INK can help with certain functions within Affinity. Please try disabling this, not only externally but also through Edit>Preferences>Tools and uncheck 'Use Windows Ink'.
Does this work better for you?
talha_psd got a reaction from Dan C in Fill Tool tolerance goes back to 1% automatically