Same issue here with Safari on iOS 15 and also MacOS Monterey beta7. On MacOS Chrome works fine.
It is a websocket server based on Espressif ESP32 hardware with a simple webserver built on the lib: https://github.com/me-no-dev/ESPAsyncWebServer
Setting safari =>Advanced=>Experimental Features=>NSURLSession WebSocket to off solves the issue. I can connect one of the devices for testing to the public internet if that helps.
ArjenH
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