Is knee locking common when bending your knee after straight legs raises (physio) to another exercise; 11 days post op from partial meniscectomy?

Yes and no. I doubt you have true locking. The most likely "locking" you are experiencing is related to patella tracking. Your knee cap is sub optimally moving in its track/groove. This can improve with therapy and rehab of your quads etc. For best diagnosis ask your surgeon.
No. If you have had a recent arthroscopic surgery, knee locking is potentially worrisome. Go back to your orthopaedic surgeon for re-evaluation.