Default value for system Property glide.ui.m.allow_classic_mobile_app is set to FALSE post upgrade to Paris instance.
1. Login an Orlando instance.
2. Create few entries in sys_mobile_devices with appId com.servicenow.servicenow and com.servicenow.servicenow-internal.
3. Go to Application OAuth - toggle classic app Oauth active flag to FALSE and then again to TRUE (save it).
4. Upgrade the instance to Paris. Note that Classic App OAuth is active=true but property glide.ui.m.allow_classic_mobile_app is still false.
This problem is under review and targeted to be fixed in a future release. To receive notifications when more information becomes available, subscribe to this Known Error article by clicking the Subscribe button at the top right of this form.