Squats Buttwink?!

[M-Love]

Hello,

Can someone please look at my Squats? I have had some low back pain after squats and filmed myself and it looks like a buttwink is my problem. I have tried to sit more back with my ass and shove my knees out. But it did not help. Is my technique a problem? Is the buttwink a problem?
Here are a few videos.

100kg and Romaleos 4
trim266DD137-A392-4E15-995D-4A525B666795.MOV on Vimeo

100kg Belt and Romaleos 4
trimB516929F-48A6-4DAE-A050-B863B26D57BA on Vimeo

120kg Belt and Romaleos 4
trim8B7E35FC-E703-498C-9625-F2C840E8B0CC on Vimeo

Flats and bar only 1
trimA1875A6E-D3C6-4C7A-AD35-5895F4319A30.MOV on Vimeo

Flats and Bar only 2
trim1E9F27FF-E8DA-4ACC-855C-1EA48D2F8FC0 on Vimeo

Highbar just for fun
https://vimeo.com/467489658

[Hayden-William Courtland]

Please post another video in lifters with about 80% of your working weight and (see the sticky) make sure your entire body (including both feet) are in the shot. Try and wear light colored clothing as well.