Hi @nimbus
It appears that a similar question was addressed sometime back.
One of the suggestions that was provided was to possibly move some of your calculated fields to the dataset layer. See if there is a possibility to move some of your calculated fields to dataset.
I am not sure why you are getting the error when trying to remove a calculated field. You could try @Xclipse 's suggestion to removing the cache and see if that resolves, otherwise you may have to approach AWS resources for help.
Regards,
Giri