Interesting. Is the website in ‘Add to Homescreen’ mode or viewed normally in Safari?
I haven’t seen that happen before – I would think that if it was just too heavy for the iPad, the browser would just crash. Taking you back to the login is odd as it’s almost like it doesn’t realize you are logged in yet. And the fact that you can load the user page and dashboard, but the loading spinners show made me think it’s loading the app but can’t connect to the database (which is why I asked about network firewalls and other devices).
If the device is still running iOS 9.3.5, then it’s likely quite an old device and not an ideal candidate for dashboards since the performance might not be amazing, but I’ve seen other people post in the community that they are using iOS 9.3.5 devices.