I went through and tried to fix and replace all legacy code of previous ionic versions. Currently at version @ionic/angular 7.8.6.
When building for SSR, and starting the app, the console prints out those warnings, accompanied by hundreds if not thousands of lines of cryptic dom code.
I don’t believe my code is responsible for the warnings, since I inspected the HTML and found slot=“helper” is only present in some commented out code, that is generated from Ionic components. Needless to say, I don’t use any illegal attributes in those components (i.e. ion-checkbox).
The warnings are a nuissance for two reasons, the app loads initially only after all the console warnings are printed out, which takes a few seconds longer. Secondly, the logs on the server are full of those logs, making it harder to read and taking up space.
My suggestion, fix it or provide a way to disable them. Or at least provide a better hint if there really is something wrong with the way I implemented Ionic components.