Selecting the default project in Toggl Button Chrome extension settings results in the default getting saved and attached to new time entries that don't have any project selected.
Default does not get saved nor attached to any new time entries.
Try to save a default project in extension settings and start a new time entry or check extension settings again after thinking you've saved them.
This is also an issue on Windows 10 (1803), Chrome 69, Extension v.1.11.1
Reported also by user 3523176
Reported by two users on Chrome Web Store
Reported by additional Chrome user on latest stable build
I still had this on v 1.17.1. Fixed by removal of extension, restart Chrome, re-add extension.
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This is also an issue on Windows 10 (1803), Chrome 69, Extension v.1.11.1