Many people have been asking about / requesting
I know Paperpile team is working hard to resolve some of those issues, but for now the solutions are limited, and the issues above have been around since around 2014. Here's a practical workaround to get all of those features, today and for free. I know I am going to mention an alternative platform, but I hope it's ok, since it does not diminish the relevance and superiority of Paperpile in Google Docs.
Here's what you can do: you can synchronize Paperpile Google Drive folder to the computer using Google Backup and Sync, install and register with Mendeley, and configure Mendeley to watch the Paperpile folder containing the PDFs of the paper synchronized to your computer. This way you have full functionality on the desktop - search, read, annotate, generate citations in Mendeley (sans ability to use Paperpile in Google Docs offline mode), you have a very capable app on your mobile platform (Paperpile mobile app is nowhere near the one from Mendeley), and when you are back online - you can use Paperpile just for Google Docs. You also get integration of your Paperpile library with MS Word via the Mendeley plugin.
I think Mendeley and Paperpile are complementary, and can help rid of major headaches. Maybe Paperpile does not need to invest effort into the tools that are robust and working well in Mendeley?
Disclaimer: I am a member of the "Mendeley Advisor" community, but I am not a member of the Mendeley/Elsevier team. I've been a user of Paperpile for at least 3 years now, and have been using Mendeley for many years before I switched to Paperpile as my primary reference manager.
I do hope this post is ok with the Paperpile team. I just want to help the users here.