Let me start with the second issue, In order to get OTOs to automatically redirect to next steps follow this tutorial:
You'll need to configure your Paypal account to accept auto redirections just once.
For the second issue, i am not aware of it, though probably you might be clicking the OTO button too fast before the page loads?! (which your customers won't be doing), but still even if that's the case the Paypal App will try to load the paypal checkout on your popup...
thus, try to wait for the page to fully load before clicking the upsell button, or PM me or anyone of the team the link to your order form and oto page.
hope that solves your problem