UI5 app crashes searching for deployed resources while served locally - sapui5

Question

I am using the UI5 Tooling (version 2.14.9) in order to serve locally a project along with its custom library. Both projects are developed with OpenUI5 version 1.84.
My ui5.yaml is configured as follows (only relevant parts are reported)
specVersion: "2.6"
metadata:
name: "launchpad"
type: module
resources:
configuration:
paths:
/my/app/: packages/my_app/webapp
/resources/library/: packages/library/src/my_library
server:
customMiddleware:
........
- name: ui5-middleware-simpleproxy
afterMiddleware: compression
mountPath: /XMII/
configuration:
baseUri: "http://ip:port/XMII/"
username: "user"
password: "pw"
In my index.html:    
<script id="sap-ui-bootstrap" src="..."
data-sap-ui-resourceroots='{
"my.app": "./",
"my.library": "/resources/library"
}'
...
></script>
The app crashes because it tries to load some of the library files on the deployment server rather than locally and gives me a 404 - File not found error. The library is fully served by the "ui5 serve" command (also the files that the app is trying to reach on the server) and a lot of its files are correctly loaded from the local directory so I can't find a motivation for this behavior.
I'm not in a Fiori environment (I'm using VSCode and not SAP BAS) and I triple checked namespaces when importing in the app files from library.
EDIT
I found a partial solution which confuses me a lot: I added in my bootstrap script a new alias pointing towards the same resource and changed the reference (only for my crashing imports) and now all files are loaded locally.
But why????
<script id="sap-ui-bootstrap" src="..."
data-sap-ui-resourceroots='{
"my.app": "./",
"my.library": "/resources/library",
"library": "/resources/library"
}'
...
></script>