Outlook mobile app - shared mailbox send as intermitten and broke.

i have dozens of users across the enterprise using outlook mobile app, who areaccessing and sending as  store shared mailboxes. in the last 3 weeks its all gone to crap and the app is broken.  i cant get support from support.office.com who tells me to use MY outlook mobile app to open a case.   as there is not web support and they cant transfer it.  the mobile app tech responds once a day at 3 am. my time. and refuses to escalate. 

i have had users uninstall /reinstall. sign out/ sign in/  remove the shared mailboxes. re add them. and nothing resovles more than an hour or day. 
clear issue. HELP
this affects outlook mobile app NOT outlook on the web.