There are applications using the following incorrect combination of the bootstrap URL variants in the sap-ui-bootstrap script tag:

<script id="sap-ui-bootstrap" src="<host or destination name>/<UI5 version>/resources/sap-ui-cachebuster/sap-ui-core.js"

E.g.: UI5/openui5#3617 (comment)

Recently, applications using this pattern have started to fail. But this is not a UI5 or CDN issue.

Using /sap-ui-cachebuster together with a fixed UI5 version defeats the purpose of cache busting and has never been a valid or supported approach. The underlying infrastructure, that serves UI5 resources, may change at any time while ensuring that only documented and supported bootstrap options keep working. Applications must not rely on this mix working accidentally but use either /sap-ui-cachebuster or one of the other options described in Overview of Bootstrap Base URLs.