The culprit was a SpaceX Falcon 9 rocket launching the Transporter-14 satellite rideshare mission.

Stargazers in Europe spot a strange cloud from SpaceX Falcon 9 rocket launch

Source: space
Source Link: https://www.space.com/stargazing/stargazers-in-europe-spot-a-strange-cloud-from-spacex-falcon-9-rocket-launch