Re-Starting Insanity Workout - Injury Advice Required

I have done Insanity I guess three times now...My advice would be to use floor mats, either get some of the puzzle piece ones and tape them together solidly, or at a minimum use a jump mat. The puzzle pieces made a big difference for me, just with the repetitive impact. Also...good shoes (I know there are some folks out there doing this barefoot, etc...hats off to you, I would if I could, but it isn't appropriate for me and many others).

Part of it may be your form/technique and part of it may be a need for a softer landing surface, either floor mats or better shoes.
On the other hand, it may also be the nature of the beast.
Insanity is designed to be high impact, hence it will take its toll on those body parts absorbing said impact. I tried doing the Insanity 60-day calendar, and would always develop increasing discomfort in my knees, ankles, and lower back.

Now, with some trial and error, I have abandoned the idea of ever trudging through the included 60-day program, doing Insanity every day for 2 months, but instead will incorporate Insanity into my workout video rotation. I might do a day or two of Insanity this week, and then no Insanity next week, or some rotation of that nature.

It works for me, and has alleviated the stress placed on those body part.

I recommend modifying the moves to suit your fitness level. I took out some of the jumps in Insanity b/c it was hard on my knees. Instead of doing a plyo jump I do squats or alternately raise my legs into the position it would be in during the jump (I know that made no sense and I'm sorry). Check out T25, it has a modifier. And the new Insanity Max 30 has a modifier as well.