I just tried disabling secure app spawning again, reboot the phone, and then tried the app again and it works!
It's very weird that I tried this earlier and it didn't, so I wouldn't celebrate just yet.
Often buggy apps will act up with secure app spawning, but disabling it doesn't actually get rid of the issue, it just makes it a rarer occurrence.
This happened earlier in the year with Tor Browser and it turned out the issue was not secure app spawning - it was just making the bug happen more often. They had to fix the big on their end.