Inconsistent NYC coverage report - babeljs

Question

All of a sudden, I'm getting very inconsistent nyc coverage reports, locally, and running in CI with Travis.
When running NYC, it fails locally, and nearly passes on Travis.
More details and config:
package.json bits:
"scripts": {
"build": "webpack --mode production",
"lint": "eslint src/",
"test": "nyc mocha --exit --forbid-only",
"verify": "npm run lint && npm run test && npm run build"
},
"dependencies": {
"core-js": "^3.26.1",
},
"devDependencies": {
"#babel/core": "^7.20.5",
"#babel/plugin-transform-runtime": "^7.19.6",
"#babel/preset-env": "^7.20.2",
"#babel/preset-react": "^7.18.6",
"#babel/register": "^7.18.9",
"babel-loader": "^9.1.0",
"babel-plugin-istanbul": "^6.1.1",
"mocha": "^10.2.0",
"nyc": "^15.1.0",
"webpack": "^5.75.0",
"webpack-cli": "^5.0.1",
"webpack-dev-server": "^4.11.1"
}
babel.config.json
{
"compact": false,
"env": {
"test": {
"plugins": [
"istanbul"
]
}
},
"presets": [
[
"#babel/preset-env",
{
"useBuiltIns": "usage",
"corejs": "3.26"
}
],
[
"#babel/preset-react",
{
"runtime": "automatic"
}
]
],
"plugins": [
"#babel/plugin-transform-runtime"
]
}
.nycrc.json
{
"all": true,
"check-coverage": true,
"branches": 100,
"exclude": [
"src/constants/**/*.js",
"src/theme/*.js"
],
"functions": 100,
"include": [
"src/**/*.js"
],
"lines": 100,
"reporter": [
"html",
"text"
],
"statements": 100
}
.mocharc.json
{
"file": [
"./test/testUtils/setupTests.js"
],
"require": [
"#babel/register",
"core-js/stable",
"global-jsdom/register",
"regenerator-runtime/runtime"
],
"recursive": true
}
Problems:
When running locally, I see branches failing across a ton of files for the ELSE path not taken for the last import in a lot of files
When running on Travis, I have files with /* istanbul ignore file */ that are getting flagged for coverage (not honoring the ignore), but do not have the problem mentioned in 1
I've scoured the internet and tried different configurations. I also tried to use C8 instead of NYC, and get C8 passing locally, but it fails miserably on the server