Regular out of memory problems

I am suddenly getting regular out of memory issues on my server. This has not been a problem until the last week or so and it is now happening every day or two as reported by Fix Common Problems. I have 16GB of RAM and the Dashboard shows 45% used but Dynamix System Stats plugin shows <1GB free and 4GB cached so I don't know why they don't agree. I don't have any VMs running but I do have a handful of docker containers (the biggest one being Crashplan using ~4GB RAM a

Remember this the amount of RAM that is reserved for 'delayed' writes to the hard disks. All OS's do this. The reason for this 'feature' can be easily explained. Back in the day when 80386-20MHz was the king of the hill, when a program like a word processor did an auto-save of a document, if you were typing all of a sudden the letters would stop appearing on the screen. When the save was complete, they would suddenly be there (hopefully). Needless to save, this was very disconcerting to most