The error `Cannot add property 0, object is not extensible` started appearing everywhere

Question

This error started appearing everywhere in our codebase out of nowhere. Few harmless looking PR's, no package updates nothing.

From my understanding, this error appears when manipulating a frozen array/object. There's no Object.freeze() nor Object.preventExtensions() in any of our codebase. It feels like most objects became frozen though. How come, it beats me.

Example:

const addOrUpdate = (array: IColumnHiderLocalStorageItem[], element: IColumnHiderLocalStorageItem) => {
 const i = array.findIndex(
   (_element: IColumnHiderLocalStorageItem) =>
    _element.configName === element.configName && _element.displayType === element.displayType);
 if (i > -1) array[i] = element;
 else array.push(element);
 return array;

};

TypeError: Cannot add property 0, object is not extensible

As now, I'm going through every merge request happened today to see anything but it's no use. Any help it appreciated.