You're quite adventurous to download and use beta software! :-) Right now it appears that there is a conflict with this beta version of iOS and the internal workings of CrewWeb. We have identified the problem and are working on a fix. There's a chance that the problem is actually just a bug in the iOS beta software. In the mean time, we are working on a fix.
When Apple releases the a subsequent revision to iOS 12.2 Beta, go ahead and let us know if CrewWeb still crashes for you.