SignalR : Warning : No client method with the name 'x' found... but the method exists !!

Hello, I'm legit flabbergasted right now. I never had this issue before. While running my SignalR-powered website, I get this warning : "No client method with the name 'x' found... but the method exists !!". But. The method exists. On the front, and back end. This is the only method in my entire project which fails to run. I've tried to remove every other method from that same react component. Not a change. I've tried to remove every logic inside the front end method, with just a console.log inside. No luck. I'm driving insane. There is absolutely, not in a gazillions years, a chance this should occur. HOW ? How, by every mean, is this happening ? Why ? Thanks.