Any idea what’s happening to my plants??

Hi, I have some shrubs in a raised flower bed that have been planted for the last 3 years and they are starting to die...
The yellow Berbaris is dropping leaves after they’ve turned brown and spotty and my Hebe’s have always been brown on the inside however they too have started to develop yellow and brown spots over the last week...
Im a novice gardener but a quick search of google indicates there may be a problem with drainage, it doesn’t tell me how to fix it though, so I’m hopeful some garden-savvy enthusiast on here would be able to give me a bit of advice please?

Photos are uploaded, any helpful information given would be appreciated