This can happen for a few reasons. Here are the most common things to check:

• Tool Opacity: Check that the opacity for your current tool is above 0%. You can find this slider on the inner ring of the Tool Wheel.
• Pressure Settings: If you use a pressure-sensitive stylus, go to Settings > Stylus and adjust your pressure settings to ensure light strokes are visible.
• Filled Stroke Smoothing: When using the Filled Stroke tool, a 100% smoothing value can reduce your shape to a line or a point. Try lowering the smoothing.
• Layer Visibility: Check the Layers menu to make sure you are drawing on a visible layer. If the layer for your tool is hidden, a popup will warn you.
• Masking: The Mask tool only affects the active layer. Ensure you are on the correct layer and that the Mask's opacity is above 0%.
• Stylus Connection: With a first-generation Apple Pencil, if it fails to connect, try charging it with a lightning adapter before pairing it with your iPad.

If you check these and still experience issues, please send us a message via the in-app Help feed.