I have seen this issue with a device as well. In my case, iOS13.4 now seems to be issuing ATT read_by_type requests (at least for manufacturer name, serial number string, an firmware revision string -- all DeviceInfo stuff), which unfortunately our FW wasn't coded to respond to. Since the FW never sent a response, the comms were blocked (only a single outstanding request is allowed) and 30s later, as expected, the phone closed the connection (LL_TERMINATE_IND). Once the FW was implemented to handle the request, all was good. However, since these messages are triggered by the OS during discovery, it's outside of the app's control. Therefore it could be pretty tricky to actually update the FW if the app can't even connect! I don't think the OS is violating BT spec (from what I can tell), but it's clear that these little changes can have a pretty big impact. It's important to test with the beta versions of iOS to get out ahead of these things, I suppose.Anyways, hope this helps someone.