I have gotten the "there doesn't seem to be anything here" error message a couple of times. Might be due to blocked or removed instances or posts (in my case at least).

Some lemmy apps (on Android) have different ways to handle things. I have been using Eterniry on and off after the recent update it got and I can tell it's much faster than Jerboa for loading images and posts but the overall UI seems slower. I tried mulitple apps as well in the past and they all have their own sets of issues which is to be expected.

The rate limiting error may also be due to you logging onto multiple devices/apps at once. A few days ago I had the same issue when I logged off and logged back in with Jerboa and Eternity within a small interval of time.

If you suspect your ISP, test with proxies and wireguard obfuscation within the mullvad app on your phone (and desktop as well if you want more accurate results, like that you can have more than just one result from one device). Try also to change your country to one that is closer to you to see if you might see some difference. It could be that you get timed out by the servers you're trying to reach with the VPN tunnel that you're using.