"Add Other" for Mobile Time Sheets is not working.
This was happening because of customizations to the "Other" choices from the OOB ones.
When the "Add Other" Page loads, it tries to pull in the Default Other choice of "Admin". This choice was inactive in the instance.
You will need to set the Mobile field to pull in your desired custom choice instead, as the default.
Once performed, everything should work as expected.
To do so, follow the steps below.
1. Navigate to the following link:
2. Change the Default Value field to your custom choice
3. Save the form
Now test in the App and the "Add Other" Page should now load and you can make your selections.