SebaD

I have Dahua XVR5108X-C and I had firmware 4.000.0000002.2 from 12-03-2019 I saw on internet, that Dahua released new firmware - 4.001.0000000.9 from 18-09-2020, so I want to do upgrade. I connect via webgui, upgrade firmware and it was mistake. The cameras are lagging now, and I don't know how to repair it. I tried to download old firmware (4.000 like earlier) and do downgrade, but it doesn't help. What can I do?