TLDR: I was mistaken, you can split bills from joint account. There’ll be a bug fix for the initial issue on Android v2.44.0 (the problem doesn’t manifest on iOS).
Just a quick follow up. I was mistaken in saying that it’s not possible to split a bill from your joint account, this is possible still.
What was the bug?
Since currently there is no “Shared” tab for joint account users, we display all pending bill splits (personal/joint account) in the Shared tab for your personal account.
The bug which manifested was that the joint account transactions weren’t loaded (and isn’t loaded until you switch to your joint account). This means that when we were trying to resolve the list of bill splits with the transactions, it couldn’t find the correct one, and then refused to render the whole screen.
Why did this work when you loaded the tab for the first time after a clean install/clearing storage, but then show a blank screen on subsequent loads?
This happens because initially, the list of bill splits is empty (until we fetch them). An empty list is a valid result, and we can combine this with the Shared Tabs and payment requests to render the screen.
The next time the screen is visited, we have the list of bill splits, one (or more) of which might be from your joint account. Because it can’t find the corresponding transaction, it won’t push the data forwards, so we’re still waiting for the list of resolved bill splits, and therefore cannot combine them with the Shared Tabs and payment requests to render the screen, which led to the blank screen.
Could this happen again today?
Yes! You can replicate this issue if you create a bill split from a transaction from your joint account and then switch to your personal account. Then if you clear data/reinstall the app, without opening your joint account to sync the list of transactions, you’ll see a blank screen.
You can “fix” it by opening your joint account to sync the transactions.
This is also why clearing data/reinstalling the app didn’t really help in this case 
it contributed to the symptom!
Can’t you just sync the joint account transactions too?
We want to avoid doing this because it’s a lot of data. Most users will not encounter this issue unless they clear data and avoid opening their joint account.
But a fix is coming?
Yes. We’ve updated the app (should be live in v2.44.0) so that it will filter bill splits for which it cannot find a transaction, so it will forward along an empty list which we can combine with the Shared Tabs and payment requests to render the UI.