Fatal error in the backend

I have a problem after updating to 1.26.2. User language: Czech, backing up to Dropbox. I’ve noticed that:
1) Updraft works normally, even though it reports an error.
2) Updraft 1.25.9 works fine, but after updating to 1.26.2, an error appears. Downgrading doesn’t help, likely due to changes in the database.
3) My user language is set to Czech. When I switch to a different language in version 1.26.2, the Updraft plugin backend works fine—which leads me to believe it’s related to localization.