I had achilles tendonitis (or 'sis'). Mornings had extremely stiff ankles too, limping for about 15 minutes before blood flowed to my ankle muscles and tendons. I had thought this was attributable to old age as many friends complain of stiff ankles in the morning.
Went to the physio after 2 months of improvement without running (but still lingering pain in the achilles and residual stiffness).
Turns out my calfs were extremely stiff and causing stress to my achilles and other foot tendons. After a painful calf massage, my tendonisis and morning stiffness disappeared within 24 hours. I now regularly massage my calf muscles and have no more ankle stiffness or signs of weakness in the achilles.