Notifications arriving late or not at all on my Sony Xperia Z5

[AC Question]

Hi there,

I'm having an irritating, on/off issue with my phone. Notifications and alerts for my apps arrive very late (sometimes over a day late) or not at all. The problem seems to be across different apps - eg, Google calendar, WhatsApp, Instagram, etc. I often get a glut of late notifications from various apps all at once (in fact, I got a heap of late ones while writing this!).

In addition, Android's Do Not Disturb function doesn't switch off according to the schedule I set (ie, if I set it to 1 hr DND, it doesn't switch off after that hour is up and I have to do it manually). Badges for Facebook alerts also don't go away after being read.

These all appear to be related in some way and have been going on for months, on and off. After the last software update, the issue did resolve itself for a while but has since come back.

I'm as up to date as Sony allows for this model (7.1.1). I've tried restarting the phone and clearing the cache for my apps, but no luck so far.

Any idea what's causing this and how I sort it? It feels like an internal clock issue but I'm probably wrong!