For any resin figure, after the fun pinning phase, the initial sanding phase, and the first primer; everything goes into a perpetual cycle to work the surface preparation. The first primer layer will reveal most if not all the mistakes in the surface. Pinholes are bubbles in the resin and when found, these are typically just the top of the bubble and just below the surface is the actual bubbles so just applying a filler over this pinhole will not resolve the issue. Rough sanding spots are hard to see in the bare resin and shows up clearly in the grey primer. Missed mold lines are also easily found after the surface has been primed.
Here’s the half hour long video of this process.