Were you using the app from ZXing team https://play.google.com/store/apps/details?id=com.google.zxi... app? Because this app was last updated in 2018, has a generic name Barcode Scanner, & has attracted hundreds of reviews like yours saying App was updated recently, & now causes Web Ads.

For a counter point, I am also using this app since 2016, & have all apps on auto update, & have never received any web add popup or notification because of this or any app.