I’ve made a fork of your test librarary, added a setupWebServer which starts the webserver on port 80. See here: GitHub - sivar2311/MinimalPlatformIOdepIssue
I’ve also created a test project see here: GitHub - sivar2311/MinimalPlatformIOdepIssueTest which calls the setupWebServer() function from fileA.h / .cpp
Everything works as expected on ESP8266 and ESP32.