Hi Stanislava,
I tested with the latest version of Monthly channel i.e. Version 1811 (Build 11029.20079) and I don’t see this behavior. I set the field to ‘No’ and then re-opened
Graphical indicator, it still shows the value set as ‘No’. I tested by creating two custom fields.

Please make sure you have all updates installed. As you are using Project Online Desktop Client, please check this
article for version information and compare your Project version and make sure you have the latest version.
If your Office version is behind, please update the apps. To know how to install Office updates, please see
Install Office updates.
If the issue persists, please confirm the version of your Project Online Desktop Client.
Thanks,
Neha