I tried again today and CashApp finally lets me login. I'm not sure what changed. I'm using sandboxed google play store and services in the private space of my owner user. Accepted network permission for the app on install, and other than that I haven't changed anything else. Exploit protection compatibility is not turned on. It is just working now.
Not sure if I should be thanking graphene devs for an update, or cashapp devs. Hurray.