In addition, please check the version of Lumin app on the iPhone and iPad respectively and see if they are running the same version.
Other than display and user interface, internally there should not be a difference for folder view retrieval on iPad vs iPhone.
What does this mean?
I appreciate the help, but I have no idea what you are talking about. I’m not using WiFi. The Lumin is connected via an Ethernet cable, which I assume is 100Mbps. Not sure how the iPhone connects to it.
In the screenshot above, the folder navigation button is the one marked as "TOSHIBA EXT".
Please make sure the 2.4GHz and 5GHz WiFi in router have different SSID (names). Then connect the iPhone to the two WiFi SSID one by one, kill Lumin app, relaunch it, and retry. See if there is one WiFi SSID that works better than the other for your iPhone.