ENONENT after updating (main.js / main.ts)

Well I’ve been speaking too quickly.
The error is back, but this time I know when it started.

First, ionic cordova build android worked like I said.
Then I wanted to try ionic serve.
Here is how it went:

D:\DocsFlo\fpAuth>ionic serve
[WARN] No local CLI detected.
       Starting with CLI 3.6, the CLI must be installed locally to use local CLI plugins.

? Install now? Yes
> npm install --save-dev --save-exact ionic@latest
x Running command - failed!
[ERROR] Error occurred while loading plugins. CLI functionality may be limited.

And then, I ran ionic serve again and got ENOENT back. Retried build for android:

D:\DocsFlo\fpAuth>ionic cordova build android
Running app-scripts build: --build --iscordovaserve --externalIpRequired --nobrowser

[16:09:15]  build dev started ...
[16:09:15]  clean started ...
[16:09:15]  clean finished in 7 ms
[16:09:15]  copy started ...
[16:09:15]  transpile started ...
[16:09:21]  transpile finished in 6.49 s
[16:09:21]  preprocess started ...
[16:09:21]  deeplinks started ...
[16:09:21]  deeplinks finished in 140 ms
[16:09:21]  preprocess finished in 145 ms
[16:09:21]  webpack started ...
[16:09:22]  copy finished in 7.54 s
[WARN] Error occurred during command execution from a CLI plugin (@ionic/cli-plugin-cordova).
Error: D:/Userfiles/fgoumot-labesse/Documents/fpAuth/src/app/main.ts
Module build failed: Error: ENOENT: no such file or directory, open 'D:\Userfiles\fgoumot-labesse\Do
cuments\fpAuth\src\app\main.js'
    at Error (native)

EDIT: I confirm.
I just ran npm install again, and I got this:

D:\DocsFlo\fpAuth>ionic cordova build android
[WARN] No local CLI detected.
       Starting with CLI 3.6, the CLI must be installed locally to use local CLI plugins.

? Install now? No
[WARN] Not loading local CLI plugins in global mode. CLI functionality may be limited.
> cordova build android
√ Running command - done!

I skipped the rest, but it built successfully. SO it seems the error comes when I say yes.