Hello,
I think I have got to the bottom of this, I saw a physio a number of times and we kept addressing issues, but still got no better. I have been tweaking things myself and came across something bizarre...

My Psoas on my left side seems very weak/inhibited. I fail on Psoas strength tests (cannot hold knee above 90 degrees for any length of time, TFL cramps from compensation). Engaging the Psoas makes my whole body solidify and all the muscles engage.

I think it may be from when I dislocated my left patella when 15 and again when 17. I was put in a plaster cast from hip to ankle but being a foolish youth I didn't used to use my crutches, instead walking the couple of miles to school and back having to swing the cast round.

Another thing I noticed, any posterior chain/hip dominant work makes my legs go as heavy as lead and lose some function. Any hip flexor work and they feel light and nimble.

Has anyone come across this? What would be the best way to stregnthen/reeducate the Psoas, particularly it's stabilising function? (I have been doing shoulder presses from a v-sit that seem to do this a little)

Thanks for any help.