For future travelers who happen upon this question in a desperate grasp at straws (like I did):

We have existing code (LWCs embedded in an Aura component) that has not been touched in a while, but on which we suddenly started to get a Component Error > Script Error that looks a lot like the OPs. This (thankfully) was only occurring in some sandboxes.

There seemed to be no rhyme or reason - in some sandboxes we had done recent dev work (but not on those components), but not in others. We finally discovered in the Setup Audit Trail where someone from Salesforce had checked Session Settings > Enable Content Delivery Network (CDN) for Lightning Component framework. (It appeared in the Audit Trail as A Salesforce employee changed 'AuraCDNPref' from 'false' to 'true' when using Manage Org Preferences.)

After unchecking Enable Content Delivery Network (CDN) for Lightning Component framework, we no longer got the Component Error.

Knowledge Article 005115596 (https://help.salesforce.com/s/articleView?id=005115596&type=1), titled, "Salesforce Lightning CDN Preference Auto Enablement" and which as of this writing is showing published 31 July 2025, indicates that Salesforce decided in their infinite wisdom to go around enabling this for everyone. In this article it states,

As this only impacts Salesforce owned content, we are enabling the org preference to be ON for customers that have the preference set to OFF. There is no required action that needs to be taken as this will be enabled by Salesforce.

I filed a Case, and in it said that I want to refute the "this only impacts Salesforce owned content" statement.