Can Spondylolisthesis still worsen if I have no pain?

1 year ago I started getting back pain and found out I had bilateral pars fracture on my L5 vertebrae. I was told to stop all sports and activities that put stress on my back for 6 months to allow my back time to heal and to make sure my spine wouldnt slip. During this time I had quite a lot of pain even though I didnt play any sports. After the 6 months I went for a check up and found that my spine had slipped 4mm forward and the fracture still hadn't healed. Now, it has been 1 year and I have been fully involved in sports for the last 6 months and am experiencing almost no pain at all and am able to play as much as i want. Occasionally my back will hurt a bit but is fine by the next day. MY QUESTION is, Can my spine still be slipping forward even if I have no pain or symptoms? Is it dangerous that I'm playing sports with this injury? btw I play soccer