I've been using a Tokina 11-16mm 2.8 lens on my Nikon D5100 for a couple dive trips with great results. Two trips ago, I found the Iris vanes would stick open on a dive, resulting in over exposure. Same thing happened when I tried it on land. If I bumped the camera, the vanes would close. I sent it for repair and they said the vanes were sticking and they repaired it. I had used the lens since then for some night sky shots - wide open aperture - with no problems but no diving due to Covid restrictions. I took it on a recent trip and found it was sticking again, both underwater and on land. When I remove the lens and worked the iris control arm, I get no sticking. Tried it on two D5100s. Has anyone seen this happen with this lens? I hate to put any more money into it if I can't be sure it works correctly.