That log was taken just after a full, clean install of LibreELEC as I'd hoped that would cure it but it didn't. Memory is fine as its brand new and I'd checked it on another system just to be sure.
In a new development though, I've cured the problem by deleting my advanced settings file which had cache related settings in it. However I still get some buffering on larger files a few minutes into the movie starting. It doesn't seem to matter what adjustments I make to the advanced settings file unless I delete it completely the behaviour above comes back.
Any ideas?