We have a private Prosody server on a VPS. The device issue may have been a setting you needed to change on your clients. By default there’s a built in delay when sending notifications to multiple devices, so whatever is seen as your active device will get the updates in real time and the others won’t. I have all mine set to no delay and all the messages sync instantly on PC and phone, assuming the phone isn’t doing any type of power or data saving that messes things up.