applications – BBM Android Chat Lost After Android Crash

I've recently had problems with Android (5.0), and the BBM app seems to be particularly volatile and could be causing accidents.

I had only one contact and a chat history with this contact, and the contact and chat history disappeared. If I check the dedicated BBM folder on the device's storage memory, the photos and chat documents are always present.

My question is: in BBM, if you delete a contact, will the other phone delete the contact and the chat? Or is it probably due to data loss in the crash of Android, and if so, where would I usually find the history of the discussions to investigate?