Um, no - The GDPR treats the simple act of storing personal data as 'processing', so turning off the service while still keeping the data resolves nothing. It doesn't even matter if you take the data offline, or temporarily obfuscate it.
But compliance isn't binary. I'm sure the data protection authorities understand the difference between “LOL I'm already noncompliant so I'll just continue business as usual” versus “Working hard to fix this – in the meanwhile, let's prevent covered Subjects from sending us more data until we are prepared to handle it compliantly.”
You can tip off the regulators if you believe that there is a violation and they will then investigate it.
Instapaper is giving a pretty good reason to be suspicious.