In order to access your website’s information via Google Search Console, you first need to verify your ownership of the site. You may already be aware that there are several methods you can use to do this, and one of those methods is via Google Tag Manager.
Google has just confirmed it fixed an issue with the Google Tag Manager method of verification via Twitter >here<
Google said you may need to re-verify your site or property in the Search Console if you were using the Google Tag Manager verification method. Google state that the issue “should be solved by now” and if you have lost your ownership status, a simple re-verification fix it.
As mentioned at the start, there are several methods you can use for the verification process, but if you used Google Tag Manager, you need to double check your properties.