"need a struct tag for tfsdk" ... but all structs have tfsdk tags

Trying to make a Terraform Provider and been trying to trace this all day. All of my model structs have “tfsdk” tags, similar to what you see below. When running “terraform apply” to test out what I’m building, I get an error:

Error: Value Conversion Error
│
│   with render_project.my-project,
│ An unexpected error was encountered trying to convert from struct value. This is always an error in the provider.
│ Please report the following to the provider developer:
│
│ error retrieving field names from struct tags: : need a struct tag for "tfsdk" on Environments

Here’s my model for a “project”:

type ProjectEnvironmentModel struct {
	Id           types.String `tfsdk:"id"`
	Name         types.String `tfsdk:"name"`
	ProjectId    types.String `tfsdk:"project_id"`
	DatabasesIds []string     `tfsdk:"databases_ids"`
	RedisIDs     []string     `tfsdk:"redis_ids"`
	ServiceIds   []string     `tfsdk:"service_ids"`
	EnvGroupIds  []string     `tfsdk:"env_group_ids"`
	Protected    types.Bool   `tfsdk:"protected"`
}

type ProjectModel struct {
	Id           types.String              `tfsdk:"id"`
	Name         types.String              `tfsdk:"name"`
	Environments []ProjectEnvironmentModel `tfsdk:"environments"`
}

I’ve gone through our entire codebase, and everywhere we define a struct we have a tfsdk tag on every field. I’m very puzzled as to where this error is coming from.