Beyond the issues of aerating after yeast addition, directly pitching dry yeast, the FG, and capping issues, how do you add the priming sugar? Maybe you said it and I missed it. If you're just adding the dry sugar to the bottling bucket before or after racking the beer in, then there could be an issue of the sugar not fully dissolving. Try making a simple syrup of the priming sugar by adding the sugar to water and boiling it to fully dissolve the sugar, then cooling it to room temp and then adding it first to the bottling bucket and racking the beer on top of it. Give it a good stir without oxygenating the beer and then bottle. This will ensure a better homogenization of the sugar and make sure some bottles aren't over or undercarbed.