Leave site? Changes you made may not be saved

Hello,

When I open a WP (5.6.1) page for editing and click somewhere – without changing anything! -, I still get the message “Leave site? Changes you made may not be saved”.
The suggested change in “autosave.js” here does not change this behaviour.
I work with CPT’s and ACF’s, but in WordPress 5.4.2 it worked correctly, i.e. the message only came up when I actually changed something.
Does anyone have an idea?

Kind regards, Michael