I have also had Roon iPad app v1.6.00390 spontaneously crash on startup – and I have been able to replicate (one set of) conditions which cause it to do so. Once it has crashed, it continues to do the same until the app is removed and reinstalled, or circumstances are changed (see below).
I have also managed to get the Mac app (v1.6 build 390) to crash under the same circumstances. This, also, continues to crash until I can change the circumstances.
Luckily, the iPhone app is resilient to this particular bug, so I was able to wrest control back!
The problem occurs when I select a radio station called “Audiophile Baroque” under Internet Radio. The website is http://stream.psychomed.gr and the stream URL is http://8.38.78.173:8045/ .
A moment after selecting this station, the app crashes. On restarting the app it immediately crashes again. The Mac app crashed as soon as I selected the room that had that source. The only way to get back control was to go on the iPhone app and change that room to play a different source.
I do not think this is endpoint (player) related: I have replicated this on a Lumin D1 and a Linn Klimax DS. Roon Core is ROCK version 1.6 build 390; Roon OS version 1.0 build 159.