Electrical – Lights not working after replacement

I have 5 lights all have their own switch. 2 upstairs 3 downstairs all run off the same circuit. I replaced the downstairs light first. Checked to see if it worked and it did. So I moved upstairs replaced the light up stairs and it also worked. Went downstairs and have no power to 3 of the lights and the outlets don't work either.

I put in the old fixture and now that doesn't work either. I am not a expert by any means.

Here is a photo of the downstairs light.

Edit
After checking the bundles again i get 120v when touching the black bundle to ground. Also getting 120v when checking the white bundle to ground. I must not have been touching the white proper when checking the 1st time. There is no power to the fixture or to the switch that controlled the light either.

After messing with the two fixtures and ensuring I didn't have a loose wire. (It kept showing open neutral). Turns out it was a plug outlet that was the problem. When I had first checked the plug with the tester it told me it was correct. When I pulled the outlet out the burnt wire pulled out of the backstabbed outlet. Thanks everyone for their help.