Sadly closed my Monzo account down recently after applying for a joint account with my partner and being denied with no explanation (both long term users, good credit etc). Apparently a common story. Opened a Starling account and got one straight away. It's a shame because the Monzo user interface is miles better.
Starling is no better, you were just lucky. I found Starling customer service appalling. Basically "go somewhere else if you don't like it".
I did try an open a Starling account once but they claimed my phone number was already linked to an existing account, which I found strange and wasn't prepared to jump through the hoops required to prove otherwise.