This is the first iPad in which I have never needed to restart, kill an open app, nor witness an app crash constantly. The iPAD PRO really is a great device! If it's constantly crashing on you, best to do a full reset/wipe and start from scratch. Always worked best this way.
I can have 15 tabs open in safari leave it this way for 2 weeks and come back daily to safari and have never had it crash once. I use spark mail now but the default mail app never crashed on my IPP either.
I have the IPP cellular model, btw.