The HMR API doesn't work with modules loaded with ssrLoadModule — if the module is invalidated, the next time it is loaded it will be instantiated anew, but import.meta.hot.dispose callbacks in the old module won't be executed.
This results in things like leaked memory and blocked ports.
Clone this repro, npm install, then node index.js. Visit https://localhost:4567. You should see 'hello!'. In the terminal, you'll see some logs:
module has been alive for 1 seconds
module has been alive for 2 seconds
module has been alive for 3 seconds
module has been alive for 4 seconds
module has been alive for 5 seconds
Make a change to src/index.js. The terminal will clear, but the messages will keep coming:
module has been alive for 6 seconds
module has been alive for 7 seconds
module has been alive for 8 seconds
module has been alive for 9 seconds
module has been alive for 10 seconds
Reload https://localhost:4567. The change will have taken effect, but the import.meta.hot.dispose callback was ignored, so now we have two live copies of the module:
module has been alive for 1 seconds
module has been alive for 11 seconds
module has been alive for 2 seconds
module has been alive for 12 seconds
module has been alive for 3 seconds
module has been alive for 13 seconds
module has been alive for 4 seconds
module has been alive for 14 seconds
module has been alive for 5 seconds
module has been alive for 15 seconds
As soon as the module is invalidated, import.meta.hot.dispose callbacks are called.