I've got a Raspberry Pi 2 running Raspbian (can't remember the exact date but it's something from early February 2017) and when connected to my router (TP-Link TD-W8970) it fails to get a DHCP allocated address more often than it succeeds (gets one maybe one in five boots).
Because of how the box is being used it needs to be on a fixed IP, but I prefer to assign this at the router level rather than setting up the device individually.
The Pi has been fully updated/upgraded so all packages are up to date.
How do I go about diagnosing why the Pi fails to get an IP on boot?
For the record, as a temporary fix, I set a fixed IP address in
/etc/dhcpcd.conf but I want to avoid this if possible.